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ADVERTISEMENTS. 


THE  .  .  . 

United  Alkali  Co., 

LIMITED. 

Telegram*: —  JAMES  STREET, 

“UBIQUE,  LIVERPOOL.” 

T  n  7rnn/^rtT 


FRANKLIN  INSTITUTE  LIBRARY 

PHILADELPHIA,  PA. 


11 


THE 

Indcrgromul  Wafer  frfismaiion  3»ss«iafinn 

FOR  THE  PROTECTION  OF 

the  underground  water  supply 

OF  THE  COUNTRY. 


Members  of  the  Executive  Committee  : 

R.  B.  Berens,  J.P.,  Chairman.  E.  H.  Joynson. 

Lt. -Col.  English,  F.G.S.  William  May,  F.R.G.S  FGS 

A.  M.  Fleet,  J.P.  A.  E.  Reed. 

Secretary : 

Clayton  Beadle,  F.R.  Met.  Soc.,  F.C.S. 

Solicitors : 

Messrs.  May,  Sykes  &  Co., 

Suffolk  House,  Laurence  Pountney  Hill,  E.C. 

Parliamentary  Agents: 

Messrs.  Sherwood  &  Co., 

7,  Great  George  Street,  Westminster,  S.W. 


y^mong  the  chief  objects  of  this  Association  are  (i)  to  suggest  the 
best  course  to  be  adopted  for  preserving  the  water  supply  under 
the  special  circumstances  of  any  particular  case;  (2)  to  suggest 
the  best  position  for  locating  pumping  stations  with  a  view  of  doing 
as  little  injury  as  possible  to  local  interests;  (3)  to  suggest  the  best 
course  to  be  adopted  in  storing  for  domestic  purposes,  the  ordinary 
rainfall,  and  (4)  to  take  all  possible  steps  to  prevent  Water  Com¬ 
panies  from  obtaining  money  and  powers  from  Parliament  for  the 
erection  of  pumping  stations  in  districts  where  there  is  a  shortage 
of  water,  and  where  such  pumping  operations  threaten  to  deprive  the 
inhabitants  of  the  district  of  their  natural  supply. 

For  publications  aild full  particulars  apply  to 

The  SECRETARY ,  /y,  The  Boro',  London  Bridge,  S.B 


Chapters  on  Papermaking 

VOL.  I. 


COMPRISING  A  SERIES  OF  LECTURES  DELIVERED  ON 
BEHALF  OF  THE  BATTERSEA  POLYTECHNIC 
INSTITUTE  IN  1902. 


BY 

CLAYTON  BEADLE 


Lecturer  on  Papermaking 
before  the  Society  of  Arts ,  1898  and  1902  ; 
at  the  Papermakers'  Exhibition ,  1897  ,*  at  the  Dickinson 
Institute ,  on  behalf  of  the  Hertford  County  Council ,  1901,  and  at  the 
Battersea  Polytechnic  Institute ,  1902;  awarded  the  John  Scott  Legacy  Medal 
and  Premium  of  the  Franklin  Institute  by  the  City  of  Philadelphia , 
and  the  Gold  Medal  of  “ La  Societe  pour  I  encouragement 
de  V Industrie  Nationale  "  of  Paris ,  and 
other  Medals  and  Awards. 


NEW  YORK 

VAN  NOSTRAND  COMPANY 

23.  MURRAY  AND  27  WARREN  STREETS 


LONDON 

CROSBY  LOCKWOOD  AND  SON 


1907 


CLO/OS 


•  •  •• 


THE  :  .ETTV  CENTER 
LIBRARY 


PREFACE. 


This  small  contribution  to  the  subject  of  Papermaking 
consists  of  a  reprint  of  the  ten  Lectures  prepared  on  behalf  of 
the  Battersea  Polytechnic  Institute  in  1902,  the  right  of 
publication  of  which  was  reserved  to  the  Author. 

These  Lectures  appeared  in  the  columns  of  Papeb  and  Pulp. 
Many  of  the  readers  of  that  Journal  haring  expressed  a  desire  to 
have  them  for  reference,  the  Author  determined  to  reprint  them 
in  book  form. 

Papermaking,  like  other  progressive  industries,  is  undergoing 
changes  :  what  is  new  to-day  will  be  old  to-morrow  ;  and  lectures 
on  Papermaking  must  share  a  similar  fate  ;  but  the  subjects  with 
which  these  lectures  deal  will  remain  with  us,  and  will  continue 
to  engage  the  attention  of  the  Papermakers  and  Papermaking 
Chemists  of  the  future. 

CLAYTON  BEADLE. 

Laboratories :  15,  The  Boro’, 

London  Bridge,  S.E. 

March,  1904. 


0  3  3  51 


CONTENTS. 


LECTUEE  I.  ^ge 

Examination  of  Fibrous  Eaw  Materials  for  Papermaking  7 

Moisture — Ash — Cellulose — Non-cellulose — Chemical  behaviour 
— Yield — Commercial  value — Consumption  of  chemicals — 
Chlorination — Precautions  for  treatment — Eag  examination. 

LECTUEE  11. 

Art  Papers  as  Applied  to  Process  Printing  . .  . .  . .  19 

Art — Imitation  art — Nature  of  surface — Nature  of  fibres — 
Minerals  used — Preparation  and  application  of  coating — 
Casein — Gelatine — Test  for  coating — Preparation  of  process 
blocks — -Chemical  and  physical  examination — Nature  and 
utility  of  coated  surface. 

LECTUEE  III. 

Bleaching  . .  . .  . .  . .  . .  . .  . .  . .  33 

Peculiarities  of  ultimate  fibres — Eelative  lengths — Character¬ 
istics — Nature  of  <l  chloride  of  lime  ” — As  powder — In 
solution — -Table  of  strengths — Effects  of  heat  and  time  on 
the  storage  of  bleaching  powder — Change  of  strength  on 
storage  of  solution — Chlorine  gas — Tumbler  bleaching — 
Bleaching  in  beater — -Effects  of  carbonic  acid  gas  on  bleaching 
solution — The  Thompson  process — Eau  de  Javelles— Eelative 
efficiencies  of  different  solutions. 

LECTUEE  IV. 

Chemistry  of  Bleaching  .  .  .  .  .  .  . .  .  .  . .  49 

Early  history  of  bleaching — Sun  bleaching — Ozone — The 
atmosphere  —  Its  bleaching  effect  —  Sunlight  —  Hermite 
electrolytic  bleachi  ng— “  Still  ” — 4‘  Circulating  ” — Continuous 
use  of  bleach  liquor — Temperature  of  bleach  liquor. 


5 


LECTURE  Y.  PaS® 

The  Influences  of  Moisture  ok  Paper  . .  . .  . .  63 

Effects  of  heat — Expansion  and  contraction  of  cellulose  with 
change  of  moisture — “  Sensible  ”  moisture — The  curling  of 
paper  with  change  of  moisture1 — Testing  for  “  machine  ”  and 
“cross  ”  direction  by  means  of  damping — Effects  of  damping. 

LECTURE  VL 

Chemical  Residues  in  Paper  . .  .  .  . .  .  .  . .  75 

Metallic  salts — Purity  of  ash — Lime  salts  due  to  bleach — 
Influence  of  acidity — Discharge  of  lines— Presence  of  iron 
— Reasons  for — Amount  in  raw  materials — Chemistry  of 
rusting — Prevention  of  rusting — Effects  of  iron  in  water  on 
paper — Elimination  of  iron  during  manufacture — Test  for 
iron — Iron  in  chemicals — In  finished  papers — Iron  and  other 
metallic  particles. 


LECTURE  VII. 

Chemical  Residues  in  Paper  ( continued )  .  .  . .  .  .  86, 

Definition  of  paper — Contamination  of  paper  from  raw 
materials — Lime  boiling— Removal  by  subsequent  washing — 
Impure  caustic— Fixation  of  lime  from  water  by  fibres — 
Effects  of  different  materials  added  to  the  chest — Mode  of 
testing  papers— Indicators — Chemical  condition  of  paper — 
Soluble  constituents  —  Insoluble  constituents  —  Effects  of 
metallic  residues  at  high  temperatures — Behaviour  of  iodide 
paper — Acidity  and  alkalinity  of  different  papers. 


LECTURE  VIII. 

The  Function  of  Water  in  the  Formation  of  a  Wed  of  Paper  102 

Effects  of  water  on  fibres — Flexibility — Felting  qualities — 
Elasticity  —  Shrinkage  on  drying — Removal  of  water  — 
Influence  of  temperature  when  hydraulic  pressing — Capillarity 
— Brittleness — Effects  of  rosin — Beating — Calendering  — 
Physical  properties  of  fibres. 


6 


LECTUBE  IX.  Pflge 

The  Permanence  or  Paper  . .  .  .  . .  . .  . .  113 

The  permanence  of  paper — The  cause  of  deterioration — 

Early  attempts  at  preservation — The  effects  of  the  fibre — 
Sizing — Clay — The  atmosphere — Sunshine — Temperature  and 
moisture  —  Discoloration  —  Fading  of  water  colours  — 
Organisms — Moisture — Fermentation — Nitrogenous  matter 
— Methods  of  examination  for — Liability  to  decay. 


LECTUBE  X.  (Part  1). 

Sundry  Physical  Qualities  of  Paper  . .  . .  . .  •  •  123 

The  Society  of  Arts  Committee — Their  decision — The  acid 
action  of  drawing  papers — Influence  of  rosin  and  gelatine 
sizing  on  strength — Deterioration  due  to  mechanical  wood — 

The  lasting  qualities  of  other  fibres — Composition  of  blottings 
— Effects  of  moisture  and  heat  upon  expansion — Discoloration 
of  papers  by  sunlight. 


LECTUBE  X.  (Part  2). 

Sundry  Physical  Qualities  of  Paper  ( continued )  .  . .  132 

H.M.Stationery  Office  contracts— National  Physical  Laboratory 
— Work  in  Italy — Banknotes — Work  in  LTnited  States  and 
Sweden — Climatic  and  local  conditions  affecting  requirements 
—Drawing  papers — Improvement  on  storage  of  papers — 
Effects  of  time  on  stretch  and  strength — Question  of  bulk- 
influence  of  glazing  on  bulk — Effects  of  mineral  constituents 
on  bulk — Influence  of  glazing  on  appearance — Action  of  light 
on  papers — Transparency — Opacity — Methods  for  determin¬ 
ing  opacity — Necessity  for  a  uniform  method. 


LECTURE  L 


EXAMINATION  OF  FIBROUS  RAW  MATERIALS 
FOR  PAPERMAKING. 

Moisture — Ash  — Cellulose— Non-cellulose — Chemical  behaviour — Yield 
— Commercial  value — Consumption  of  chemicals — Chlorination — 
Precautions  for  treatment — Rag  examination. 


It  will  be  noticed  on  looking  at  the  syllabus  of  these  lectures 
that  there  is  no  mention  made  of  this  subject.  The  fact  is  that 
the  syllabus  was  only  intended  to  give  a  general  statement  of 
some  subjects,  as  a  rough  guide,  which  might  be  treated  of  in  this 
course  of  lectures.  For  future  lectures  1  shall  have  to  be  guided 
largely  by  the  composition  of  the  class,  and  the  requirements 
of  the  students  who  attend.  This  I  hope  to  discover  during  the 
half-hour  devoted  to  discussion  on  the  lecture. 

I  have  long  ago  given  up  all  attempt  to  deal  with  the  subject 
of  papermaking  in  a  general  sort  of  way,  as  it  is  generally  dealt 
with  in  text-books.  I  do  not  think  it  advisable  to  attempt  to 
give  an  elaborate  and  detailed  description  of  the  processes  as 
they  follow  one  another  in  the  ordinary  course  of  papermaking, 
such  as  is  attempted  in  Hoffman’s  Treatise  and  other  text-books 
dealing  with  the  subject  from  a  general  point  of  view. 

It  is  impossible  for  anyone  to  become  a  papermaker,  or  to 
acquire  a  practical  knowledge  of  papermaking,  merely  by  listening 
to  lectures  or  by  studying  publications  on  the  subject ;  but  it 
should  be  possible  for  students  to  obtain  a  more  intellectual  grasp 
of  the  subject,  especially  if  they  are  engaged  in  a  paper  mill. 

I  understood  that  this  class  would  consist  partly  of  students 
engaged  in  paper  manufacture  and  partly  of  students  engaged  in 
large  stationery  businesses  who  desire  to  get  a  closer  knowledge- 
of  the  paper  which  goes  through  their  hands.  I  cannot  hold  out 
any  hopes  that  the  latter  will  ever  be  able  to  consider  themselves 
papermakers,  however  much  they  may  study  the  subject.  In 


8 


order  to  'understand  the  manufacture  of  paper,  and  to  be  of  real 
practical  service  in  a  paper  mill,  it  is  necessary,  of  course,  to  go 
through  the  mill,  working  in  each  of  the  chief  departments.  This, 
however,  is  only  the  privilege  of  the  few  who  are  likely  to  become 
foremen  and  managers  of  paper  mills;  the  majority  have  to  be 
contented  with  a  more  limited  experience.  It  is  possible, 
however,  that  aii  ordinary  workman  may  go  through  one  depart¬ 
ment  to  another,  as  opportunities  arise  for  his  promotion. 

I  have  always  claimed  that  it  is  important  for  any  workman 
'to  have  some  knowledge  of  the  actual  mechanical  operations 
which  he  may  have  to  conduct  in  his  ordinary  routine  work, 
and  also  of  the  operations  which  are  affected  by  his  own  labour. 
This  I  endeavoured  to  emphasise  in  my  lecture  before  the  Society 
■of  Arts.  I  regard  this  as  particularly  true  of  papermaking.  In 
many  of  the  departments  a  man’s  work  is  largely  dependent  upon 
-the  work  of  other  departments.  As  an  instance  of  this,  I  would 
mention  the  way  that  the  work  is  done  in  the  rag-house  will 
affect  that  process  right  throughout.  The  beating  also  has  an 
important  effect  upon  the  way  the  material  will  work  upon  the 
machine.  It  is  important  for  the  machineman  to  know 
something,  at  any  rate,  about  beating ;  and  it  is  important  also 
that  the  beaterman  should  know  something  about  the  way  the 
treatment  of  the  fibres  in  the  beater  influences  the  stuff  as  it 
passes  over  the  paper  machine,  in  order  that  he  may  beat  his  stuff 
to  the  best  advantage  for  the  machineman. 

It  is  evident  that  the  large  stationers  of  this  country  who 
are  engaged  in  the  selling  of  paper  desire  that  some  of  their 
staff  should  possess  some  knowledge,  at  any  rate,  of  the  process 
of  papermaking  and  the  composition  of  papers.  It  appears  to  me 
that  this  may  be  carried  too  far.  Taking  a  more  broad-minded 
view,  1  think,  on  the  whole,  it  would  be  more  to  ihe  advantage 
both  of  the  papermaker  and  the  stationer  if  they  knew  something 
about  the  difficulties  with  which  they  each  have  to  contend,  and 
without  trespassing  on  each  other’s  domains.  This  might  be  done 
in  some  measure  by  the  holding  of  classes  where  practical  subjects 
are  discussed. 

1  have  chosen  for  the  subject  of  this  evening’s  lecture  the 
preparation  of  fibrous  raw  materials.  I  think  it  is  a  subject 
which  should  prove  of  a  good  deal  of  general  interest.  The 
information  which  I  have  to  put  before  you  may  be  rather  in 
.advance  of  some  of  the  students  in  the  class,  but  as  the  lecture  is 
to  be  printed  in  the  columns  of  Papek  and  Pulp,  they  will  have 
■.opportunities  of  studying  it  at  their  leisure,  and  to  ask  me 


9 


questions  in  regard  to  same  during  the  discussion  after  subsequent 
lectures. 

If  any  of  those  who  take  notes  of  these  lectures  desire  to  ask 
any  question  whieh  deals  directly  with  the  subject  of  the  lecture, 
I  should  be  obliged  if  they  would  briefly  state  their  question  in 
writing,  that  I  may  endeavour  in  a  future  lecture  to  give  them 
information  on  the  question  which  they  raise,  or,  if  time  is  short, 
to  refer  them  to  some  means  of  obtaining  information  through 
some  publication  bearing  on  the  matter. 

The  examination  of  fibrous  raw  materials  in  a  systematic  wav 
is  outside  the  province  of  an  ordinary  worker,  and  such  work 
requires  a  good  deal  of  experience  and  special  appliances ;  but  it 
is  instructive,  as,  in  order  to  examine  the  raw  material,  it  is 
often  necessary  to  put  it  through  treatments  and  processes  more 
or  less  imitating  what  takes  place  in  the  paper  mill.  By  the 
results  obtained  from  such  treatments  and  processes,  a  very  fair 
practical  knowledge  can  be  obtained  of  the  quality  and  value  of 
the  fibres  under  treatment. 

As  far  as  I  am  aware  no  systematic  attempt  was  made  in  this 
direction  until  the  Indian  and  Colonial  Exhibition  in  1886.  My 
cousin,  Mr.  E.  H.  Joynson,  at  whose  mill  I  was  at  work  at  the 
time  of  this  Exhibition,  was  very  anxious  to  undertake,  in  con¬ 
junction  with  the  well-known  chemists,  Messrs.  Cross  &  Bevan, 
a  systematic  examination  of  the  fibres  exhibited  at  this  Exhibition. 
This  was  finally  arranged  at  a  conference  held  at  the  Exhibition, 
and  I  was  deputed  by  Mr.  Joynson  to  carry  out  the  analytical 
work  in  conjunction  with  Messrs.  Cross  &  Bevan,  of  London. 
This  work  lasted  about  six  months.  As  a  result  a  special  report 
was  issued  by  the  authority  of  the  Secretary  of  State  for  India, 
dealing  with  the  various  Indian  fibres,  and  a  further  report  was. 
issued  by  the  Colonial  Secretary,  edited  bv  Sir  Henry  Trueman. 
Wood. 

I  give  you  here,  from  the  Indian  report  above  mentioned,  the- 
modus  operandi  adopted  for  the  examination  of  the  various  fibres, 
for  the  determination  of — 

Moisture, 

Mineral  constituents, 

Hydrolysis, 

Cellulose, 

Mercerisation, 

Acid  purification,  &c. 

“  Moisture.—  All  the  celluloses  hold,  in  their  ordinary  state,  a  certain 
proportion  of  moisture,  or  as  we  may  term  it,  water  of  condition,  which 


10 


within  the  limits  of  variation  ( 1  —2%),  due  to  atmospheric  changes,  is  definite, 
and  characteristic  of  each  fibre.  It  is  noteworthy  that  the  proportion  of 
hydroscopic  moisture  is  an  index  of  susceptibility  of  attack  by  hydrolytic 
agents ;  it  is  certainly  true  that  the  textile  fibres  of  the  highest  class  are 
distinguished  by  their  relatively  low  moisture.  The  extent  to  which  this 
condition  is  applicable  will  he  seen  by  an  examination  of  the  table  of 
analytical  results. 

“  It  is  scarcely  necessary  to  say  tbat-the  moisture  is  determined  by 
drying  a  weighed  quantity  of  the  fibre.  It  is  necessary  to  raise  the 
temperature  to  110  degrees  (C.)  to  drive  off  the  whole  of  the  water.  At  100 
degrees  a  fibre  will  often  retain  1%  of  its  weight.  Owing  to  the  variations 
in  this  constituent,  it  is  expedient  to  express  all  the  results  of  analysis  as 
percentages  of  the  dry  fibre. 

“  Mineral  Constituents. — The  ash  left  on  incinerating  the  fibre  is 
■determined  in  the  usual  way.  The  proportion  is  low  in  the  iigno-celluloses, 
higher  in  the  pecto-celluloses,  and  especially  when  the  proportion  of  non- 
cellulose  is  high.  Cellular  tissue  further  contains  a  higher  proportion  of 
mineral  constituents  than  the  fibres,  and  an  admixture  of  the  former, 
therefore,  raises  the  percentage. 

“  Hydrolysis. — There  are  two  classes  of  reagents  which  intensify  that 
resolving  action  of  water  upon  organic  bodies  known  as  hydrolysis,  they 
are  the  acids  and  alkalies  of  these.  The  former,  for  the  most  part,  exert  a 
very  destructive  action  upon  the  vegetable  fibres,  and  though  the  study  of 
this  action  would  doubtless  afford  valuable  information,  it  has  not  been 
found  expedient  to  include  it  in  our  scheme  of  analysis. 

“  The  action  of  boiling  dilute  alkalies,  on  the  other  hand,  effecting  a 
■simpler  resolution,  and  involving  very  important  points  in  the  practical 
applications  of  the  fibres,  gives  results  which  form  a  necessary  part  in  their 
diagnosis.  A  convenient,  though  of  course  arbitrary  method,  has  been 
selected  as  follows:— -The  fibre  is  boiled  (a)  for  five  minutes  in  a  solution 
of  caustic  soda  (1  per  cent.  Na20),  washed,  dried,  and  weighed.  The  loss 
of  w'eight  presents  the  proportion  of  the  fibre  which  yields  to  the  solvent 
action  of  the  alkali.  (b)  In  a  second  portion  of  the  fibre  boiling  is  continued 
for  one  hour.  The  loss  of  weight  is  an  indication  of  the  ‘  degrading  ’  action 
of  the  alkali.  In  many  of  the  pecto-celluloses  the  hydrolytic  action  of  the 
prolonged  boiling  is  such  that  the  non-cellulose  is  almost  completely 
dissolved  away.  Generally  in  this  class  the  loss  is  considerable,  snd  the 
difference  between  the  loss  in  a  and  b  also.  Further,  the  hydrolytic  effect  is 
extended  to  the  undissolved  portion  or  cellulose,  and  the  evidence  of  the 
hydrating  and  gelatinising  action  is  the  stiffening  of  the  fibres  on  drying,  and 
when  the  action  is  very  pronounced,  reagglutiDation  into  bundles  which  dry 
to  wiry  strands.  This  latter  effect  is  minimised  by  dehydrating  the  boiled 
specimen  with  alcohol  and  drying  at  a  gentle  heat.  The  hydro-celluloses, 
as  already  stated,  are  not  readily  attacked  by  the  dilute  alkalies,  and  it  is 
only  when  digested  at  very  high  temperatures  that  the  resolution  into 
cellulose  and  non-cellulose  is  effected.  In  either  group  it  will  be  found 
that  whatever  the  condition  of  the  hydrolysis  it  is  always  more  or  less 
incomplete,  and  requires,  for  the  isolation  of  the  cellulose,  to  be  sup¬ 
plemented  by  the  treatmeut  about  to  be  described. 

“  Cellulose. — A  fresh  specimen  having  been  boiled  in  the  dilute 
alkali  (1  per  cent.  Na„0),  is  well  washed  and  exposed  for  one  hour,  at  the 
ordinary  temperature,  to  an  atmosphere  of  chlorine  gas.  It  is  then 
removed,  washed,  and  treated  with  a  solution  of  sodium  sulphite,  which  is 


11 


slowly  raised  to  the  boil.  After  two  or  three  minutes’  boiling  it  is  washed, 
oa  a  filter  when  necessary,  though  in  most  cases  it  may  be  so  placed  in  a 
funnel  as  to  aet  as  its  own  filter,  lastly  treated  with  dilute  acetic  acid, 
washed,  dried,  and  weighed.  The  percentage  yield  on  the  raw  fibre  is  the 
most  important  criterion  of  its  composition  and  value.  We  have  already 
pointed  out  that  these  celluloses,  although  similar  in  external  characteristics, 
are  of  widely  different  chemical  constitution,  and  consequently  vary 
considerably  in  their  power  of  resisting  the  further  action  of  oxidising  and 
hydrolytic  agents.  To  follow  up  these  cellulosic  products  into  the  region  of 
specific  variations  is  a  special  study  in  itself,  and  further  investigation  must, 
therefore,  he  reserved.  It  is  sufficient  here  to  have  indicated  that  the 
various  celluloses  are  not  identical,  and  that  the  term  is  applied  to  an 
aggregate  of  unknown  components  obtained  as  the  residue  from  the 
treatment  above  described. 

Mercerising. — The  action  of  concentrated  solutions  of  the  alkalies 
upon  the  vegetable  fibres  is  an  important  feature  in  the  diagnosis  of  their 
composition  The  structural  modification  which  the  cotton  fibre  undergoes 
under  this  treatment  was  originally  studied  by  Mercer,  and  hence  the  term 
‘  mercerising,’  by  which  the  process  is  known.” 

There  must  of  necessity  be  a  considerable  variation  in  the 
modus  operandi  to  suit  the  peculiarities  of  the  fi  bre  under  treatment. 
A  knowledge  of  this  can  only  come  after  considerable  practice.  It 
will  be  seen  that  the  figures  and  recommendations  to  follow  will 
not  in  all  respects  tally  with  the  foregoing.  IVly  remarks  are 
intended  to  apply  in  a  general  sense  only,  and  that  is  all  we  can 
hope  to  do  within  the  scope  of  this  lecture. 

From  results  on  a  number  of  fibres  tested  according  to  the 
foregoing  scheme,  very  useful  conclusions  were  arrived  at,  and 
this  scheme  for  the  analysis  and  examination  of  fibres,  which 
was  originally  worked  out  by  Mr.  Cross,  was  so  valued  as  to  be 
made  a  general  scheme  by  the  Imperial  Institute  authorities  in 
their  researches  and  publications  on  industrial  fibres,  the  results 
of  which  w^ere  published  in  the  Imperial  Institute  Journal. 
With  many  fibres  which  I  have  had  occasion  to  examine  since  that 
time  I  have  made  use  of  that,  scheme  of  analysis. 

I  should  like  to  draw  your  attention  to  one  or  two  points  of 
interest  in  connection  with  the  estimation  of  cellulose.  In  the 
ordinary  papermaking  process  for  the  purification  of  fibre,  an 
attempt  is  made  to  remove  all  the  non-cellulose  matter,  and  to 
retain  only  the  cellulose  as  far  as  is  practicable.  As  a  general  rule 
this  is  done  in  practice  by  boiling  under  pressure  with  soda, 
and  then  washing  and  finally  bleaching  by  means  of  calcium 
hydrochlorite  or  bleaching  powder.  In  laboratory  practice  on  a 
small  scale,  this  would  entail  too  much  time  and  too  many  special 
appliances.  The  same  result  is  brought  about  in  laboratory  work 
by  boiling  in  the  open  with  a  weak  solution  of  caustic  soda  for  a 


12 


period  say  up  to  one  hour,  so  as  to  soften  the  fibres  and  render 
the  lignified  or  non-cellulose  portion  of  the  fibre  more  reactive 
to  treatment  with  chlorine.  The  fibre  is  then  washed  to  free  it 
from  caustic  soda,  and  is  loosely  suspended  in  a  damp  condition 
in  a  beaker  into  which  a  stream  of  chlorine  gas  is  passed.  If 
the  fibre  is  a  lignified  one,  that  is  of  the  nature  of  wood  or  jute, 
a  change  takes  place,  and  the  fibre  alters  in  colour,  but  instead 
of  the  chlorine  having  the  effect  of  bleaching  the  fibre  in  the  way 
that  ordinary  bleaching  powder  does  with  rags,  it  combines  with 
the  lignin  or  non-cellulose  portion  of  the  fibre,  forming  what  is 
called  a  chlorinated  product.  The  fibre  is  allowed  to  remain  in 
chlorine  gas  for  about  say  five  hours,  at  the  end  of  which  time 
there  should  be  excess  of  chlorine,  showing  that  the  fibre  has 
taken  up  as  much  as  it  will.  There  is  a  tendency  during 
chlorination  for  the  fibre  to  rise  in  temperature,  due  to  the 
chemical  action.  This  is  detrimental,  and  can  be  avoided  by 
surrounding  the  beaker  with  a  jacket  of  cold  water.  The 
chlorinated  product  is  now  removed  from  the  beaker  and 
immersed  in  a  dilute  solution  of  cold  sulphite  of  soda.  This 
gives  rise  to  a  beautiful  red  reaction.  The  red  compound  so 
formed  is  dissolved  out  on  heating  the  solution  after  it  has  been 
allowed  to  stand  for  some  time.  It  will  be  noticed,  therefore, 
that  the  non-cellulose  has  been  removed  as  a  chlorinated  product, 
instead  of  by  treatment  under  pressure  with  caustic  soda,  as 
would  be  the  case  in  ordinary  practice. 

When  the  boiling  has  been  allowed  to  continue  for  some 
time  the  fibre  is  washed  with  hot  water,  and  may  be  treated 
with  a  w7eak  solution  of  sodium  hypochlorite  to  remove  any 
colour  still  remaining,  then  washed  perfectly  free  from  bleach  and 
treated  with  a  dilute  solution  of  acetic  acid,  and  again  washed ; 
.then,  in  order  to  get  the  greatest  amount  of  purification,  it  can 
be  washed  with  hot  alcohol,  and  dried  off  and  weighed  at  a 
'temperature  of  105°  C. 

The  bone  dry  weight  of  fibre  so  obtained,  calculated  on 
the  original  bone  dry  weight,  gives  a  percentage  yield  of 
cellulose.  The  difference  between  this  percentage  and  the  100 
gives  us  a  percentage  of  foreign  matter  removed  during  treatment. 

There  are  many  precautions  necessary  in  conducting  this 
treatment.  Sometimes  it  happens  that  one  chlorination  is  not 
enough  to  remove  the  whole  of  the  lignin.  It  is  a  dangerous 
practice  to  resort  to  a  second  chlorination  after  boiling  with 
sulphite  of  soda,  although  this  may  be  done  if  care  is 
exercised. 


13 


The  best  plan  in  such  cases  is  to  use  bromine  water,  by 
pouring  a  few  drops  of  bromine  into  water.  The  fibre  treated 
with  bromine  in  this  way  is  said  to  be  brominated,  that  is,  a 
lignified  portion  combines  with  bromine  and  is  afterwards  treated 
with  sulphite  of  soda.  A  soluble  compound  is  produced  as  with 
the  chlorine  compound ;  the  result  is  the  same,  but  bromine  is 
a  much  safer  substance  to  use.  Instead  of  sulphite  of  soda, 
after  the  chlorination  or  bromination,  sometimes  ammonia  is  used. 
This  is  a  very  safe  chemical  for  removing  the  chlorination 
product,  and  is  a  safer  one  than  caustic  soda,  and  far  less  liable 
to  reduce  the  yield  of  cellulose. 

I  would  point  out  that  what  is  known  as  the  “  personal 
equation  ”  enters  very  largely  into  this  class  of  work.  A  great 
deal  depends  upon  the  exact  conditions  as  to  the  yield  of 
cellulose  obtained. 

It  is  necessary,  therefore,  to  have  a  good  deal  of  practice 
at  the  work. 

In  regard  to  the  estimation  of  moisture  in  the  fibre,  this  is 
generally  done  by  heating  it  at  a  temperature  of  105®  C. :  it  is 
necessary  to  go  above  boiling  point,  because  at  boiling  point  some 
fibres  still  retain  an  appreciable  amount  of  moisture.  It  is 
necessary  here  also  to  exercise  a  considerable  amount  of  care, 
because  with  some  products  oxidation  takes  place,  oxygen 
combining  with  the  fibre  and  actually  increasing  its  weight, 
besides  impairing  its  qualities. 

In  other  products,  on  the  other  hand,  there  are  volatile 
substances,  such  as  in  the  case  of  wood,  in  addition  to  moisture, 
which  are  driven  off  at  the  temperature  of  boiling  water,  but  for 
all  practical  purposes  it  is  near  enough  if  the  fibre  in  question  is 
dried  at  a  temperature  of  105°  Fahr.,  and  weighed  in  a  weighing 
tube  until  the  iveight  is  constant.  The  time  should  not  be  pro¬ 
longed  beyond  this,  so  as  to  avoid  as  far  as  possible  any  chance 
of  oxidation  taking  place. 

For  more  careful  work  and  to  avoid  the  removal  of  volatile 
substances  other  than  water,  it  is  best  to  dry  the  sample  in  a 
desiccator  over  sulphuric  acid.  This  I  have  often  done  and 
compared  with  the  method  above  cited,  and  found  to  give  very 
good  results,  although  it  may  take  longer  and  require  greater 
care.  The  amount  of  moisture  which  the  fibre  is  found  to 
contain  by  the  first-mentioned  method  will  give  some  idea  of 
its  purity ;  the  greater  the  moisture,  as  a  general  rule,  the 
greater  the  impurities ;  but,  in  addition  to  this,  the  moisture  of 
every  fibre  is  dependent  upon  the  atmospheric  conditions.  If 


14 


the  air  is  damp  the  moisture  will  be  high  ;  if  the  air  is  dry  the 
moisture  will  be  comparatively  low. 

If,  therefore,  you  wish  to  compare  different  fibres  for 
moisture,  you  should  expose  them  to  the  same  atmosphere. 
In  order  to  get  really  concordant  results  for  a  large  number  of 
determinations,  it  is  far  better  to  weigh  all  fibres  under  known 
atmospheric  conditions,  using  the  wet  and  dry  bulb  thermometer 
to  indicate  the  atmospheric  conditions,  and  always  to  adhere  to 
these  conditions  for  the  purpose  of  comparison  of  each  series. 

Having  got  some  general  knowledge  of  the  qualities  of  the 
fibre  by  means  of  the  tests  above  mentioned,  we  will  pass  on 
to  the  more  practical  part  of  the  subject. 

I  would  point  out  that  it  does  not  follow  that  if  the  fibre 
gives  a  certain  yield  of  cellulose  that  it  will  yield  in  practice  the 
same  amount.  In  practice  it  may  yield  less,  but,  nevertheless, 
it  is  a  very  valuable  guide  to  what  we  may  expect  of  the  fibre 
if  treated  on  a  large  scale. 

It  is  particularly  valuable  for  the  purposes  of  comparison. 
Thus,  if  we  determine  in  exactly  the  same  manner  the  cellulose 
in,  say,  half  a  dozen  samples  of  chemical  wTood  pulp,  we  shall  be 
right  in  assuming  that  the  one  which  gives  the  highest  yield  of 
cellulose  is  the  purest  pulp,  and  will,  other  things  being  equal, 
require  the  least  amount  of  bleaching  powder  to  make  it  white. 
[Furthermore,  it  is  approximately  true  to  say  that  if  sulphite 
wood  A  contains  5  per  cent,  of  non-cellulose,  and  sulphite  wood 
B  contains  10  per  cent,  of  non-cellulose,  B  will  require  double 
the  amount  of  bleaching  powder  as  compared  with  A  to  make 
it  white.  We  can  draw  useful  inferences  in  this  way  from  such 
work.  In  making  a  comparison  of  different  brands  of  unbleached 
pulp,  the  estimation  of  cellulose  affords  a  useful  criterion,  for  it 
not  only  enables  us  to  get  some  idea  of  the  bleach  required,  but 
also  of  the  yield  we  may  expect  of  bleached  pulp  from  each  brand. 

Turning  to  the  work  of  the  examination  of  raw  wood  in 
order  to  arrive  at  the  yield  which  the  wood  majr  yield,  it  is 
essential  that  we  take  an  average  section  of  the  wood  so  as  to 
represent  the  average  composition  of  the  trunk.  This  must 
be  done  with  the  greatest  care,  and.  in  order  to  treat  on  a  small 
scale,  we  must  get  the  wood  into  thin  shavings,  which  can  be 
done  easily  by  means  of  an  ordinary  plane.  It  is  an  extremely 
difficult  matter  to  treat  wood  in  the  laboratory  in  large  masses, 
as  is  done  in  ordinary  factories,  in  fact  it  is  out  of  the  question. 
Such  shavings,  of  course,  must  be  produced  in  the  direction  in 
which  the  fibres  run,  so  as  to  avoid  cutting  the  ultimate  fibres  as 


15 


far  as  possible.  As  explained  before  the  Dickinson  Institute, 
in  order  that  such  results  may  be  of  real  value,  we  must  take  into 
consideration  the  weight  of  a  given  bulk  of  wood  in  our 
calculations. 

Seduction  to  sawdust  should  never  be  used  as  a  means  of 
sampling  timber,  as  in  sawdust  the  ultimate  fibres  are,  more  or 
less,  broken  asunder,  and  cellulose  so  obtained  would  be  no 
criterion  of  what  we  should  expect  in  practice. 

Now,  I  will  describe  to  you  the  mode  which  I  have  made 
use  of  for  arriving  at  some  more  practical  knowledge  of  the  way 
the  fibre  would  behave  in  ordinary  practice : — 

Determine  percentage  of  ash  by  burning  1  gramme  until 
weight  of  ash  is  constant.  (Note  colour  of  ash.) 

Determine  moisture  by  drying  at  212°  Fahr.  until  weight 
is  constant ;  weighing  must  be  done  in  tube.  Determine  the 
cellulose  by  the  following  method  : — 

Boil  in  dilute  alkali  until  fibre  is  softened. 

Wash,  and  expose  to  chlorine  gas,  for  several  hours,  in 
beaker,  which  should  be  kept  cool  by  surrounding  with  cold 
water.  (Note  whether  fibre  is  changing  in  colour  in  chlorine.) 

Wash  chlorinated  fibre  to  free  from  HC1,  and  place  in  weak 
solution  of  neutral  sulphite  of  soda.  (Note  whether  magenta 
colour  is  developed.)  After  one  hour  boil  solution  until 
colouring  matter  is  dissolved. 

Wash  with  hot  water. 

Bleach  with  weak  solution  of  sodium-hypochlorite.  If 
cellulose  is  not  white,  give  further  treatment  in  chlorine  gas  or 
in  bromine  water,  but  be  careful  that  treatment  does  not  injure 
fibre.  Then  repeat  treatment  with  sulphite,  wash,  bleach,  wash, 
acidify  with  acetic  acid,  dry  at  212°  Fahr.,  and  weigh  in 
weighing  tube.  The  weight  calculated  on  the  air-dry  original 
gives  the  percentage  of  cellulose. 

Note  the  general  appearance  and  character  of  the  cellulose. 
Examine  cellulose  under  microscope  and  note  how  near  it 
approximates  to  one  or  other  of  the  various  fibres  in  common 
use  for  papermaking. 

From  the  microscopic  characteristics  can  be  judged,  in  a 
large  measure,  the  relative  value  of  this  cellulose  in  comparison 
with  other  materials. 

If  sufficient  material  is  available,  treat  1,000  grammes  in 
5,000  grammes  caustic  soda  liquor  in  a  small  spherical  revolving- 
boiler.  The  strength  of  soda  must  be  carefully  ascertained  by 
titration  at  commencement,  and  care  must  be  taken  throughout 


16 


the  treatment  that  no  steam  is  allowed  to  escape,  thus  altering 
the  liquor  in  strength.  Boil  at  100  lbs.  pressure,  and  draw  off 
at  intervals  of  an  hour  small  samples,  which  test  for  free  alkali. 
When  the  free  alkali  remains  constant  discontinue  boiling  ; 
carefully  wash  boiled  pulp,  taking  care  that  no  fibre  is  lost. 

Dry  and  weigh  pulp  at  220°  Bahr. ;  this  weight  gives  the 
percentage  of  unbleached  pulp  on  original  weight  of  fibre.  Let 
the  pulp  become  air-dry  by  long  exposure  to  air,  and  until  it  no 
longer  gains  weight ;  weigh  pulp,  and  calculate  percentage  of 
air-dry  pulp  on  raw  material ;  this  is  the  figure  that  should 
be  taken  for  commercial  purposes. 

From  the  analysis  of  the  liquor  you  know  exactly  the 
percentage  of  soda  neutralised  during  the  boiling.  Bor  the 
purpose  of  final  analysis  of  liquor,  the  liquor,  together  with  all 
the  washing,  is  made  up  to  a  known  volume,  and  the  “free” 
and  “total”  soda  are  carefully  determined.  The  difference  is 
the  soda  combined  and  used  up  by  the  fibre. 

The  original  amount  of  soda  added  is  known.  We  can  easily 
calculate  the  weight  of  soda  consumed,  and  then  see  what 
percentage  this  bears  to  the  original  weight  of  the  fibre 
treated. 

We  should  now  conduct  another  boiling  trial,  adding  soda 
slightly  in  excess  of  that  found  to  be  “consumed”  in  the  first 
trial.  The  extent  to  w’hich  this  soda  should  be  diluted  must 
depend  upon  the  condition  of  the  raw  fibre,  and  must  be  left 
to  the  discretion  of  the  observer.  The  same  pressure  is  applied 
(unless  there  is  good  reason  to  suppose  that  a  higher  or  lower 
pressure  would  be  advantageous  from  the  general  appearance  of 
the  first  treated  lot).  Samples  are  again  drawn  off  every  hour, 
and  the  boiling  continued  until  no  further  neutralisation  of  soda 
takes  place.  The  rest  of  the  treatment  should  be  conducted  as 
in  previous  trial.  The  calculated  percentage  of  pulp  should  be 
near  that  of  first  trial. 

The  cellulose  should  now  be  determined  in  a  small  portion 
of  the  bone-dry  boiled  pulp,  and  should  not  be  less  than  90  per 
cent. ;  the  ash  should  also  be  determined  in  unbleached  pulp. 

A  portion,  say  half  of  one  of  the  boilings,  should  be  carefully 
weighed  and  then  treated  with  successive  quantities  of  bleach 
solution,  equal  to  5  per  cent,  of  dry  bleaching  powder  at  a  time. 
One  quantity  should  exhaust  itself  before  another  is  added. 
Any  excess  of  bleach  remaining  after  the  colour  no  longer  shows 
improvement  should  be  determined  and  deduction  from  the  total 
added  before  calculating  the  bleach  consumed  by  fibre. 


17 


A  second  bleaching  experiment  should  be  done  as  a  check, 
adding  just  the  equivalent  of  bleach  found  to  have  been  consumed 
in  first  trial.  The  bleached  pulp  is  washed,  acidified,  washed, 
dried,  and  weighed,  and  then  exposed  to  air-dry.  Bleached  pulp 
should  be  calculated  upon  the  original  raw  fibre  boiled.  The  ash 
of  the  bleached  pulp  should  be  determined. 

Put  some  of  bleached  pulp  in  beater,  beat  carefully  and  make 
into  paper  on  hand-mould,  with  or  without  clay,  alum,  starch,  &c. 

Take  stuff  from  known  mill  furnish,  and  make  also  into 
hand  sheets,  under  the  same  conditions  as  far  as  possible. 

Compare  the  relative  strengths  and  other  physical  qualities. 
The  stuff  of  known  furnish  will  produce  paper  on  machine  of 
known  qualities ;  from  this  we  can  form  some  rough  judgment 
of  what  might  be  expected  from  the  fibre  under  examination. 

Note  the  comparative  shrinkage  of  the  sheets,  the  comparative 
felting  qualities,  and  such-like  qualities. 

Prom  the  foregoing  work  one  can  form  a  very  fair  estimate 
of  value.  Cceteris  paribus  the  raw  material  would  be  in  the  long- 
run  more  valuable  in  proportion  as  the  consumption  of  chemicals, 
&c.,  and  treatment  was  small,  the  ease  with  which  it  can  be 
manipulated,  the  cleanliness  of  the  pulp,  &c.,  &c.  The  length  of 
the  fibres,  the  whiteness  and  purity  of  the  fibre,  and  also  general 
utility  and  adaptability  are  judged  from  the  quality  of  paper  it 
produces. 

It  should  be  ascertained,  if  possible,  how  much  bulk  a 
given  weight  of  raw  fibre  will  occupy.  If  bulky,  the  freight 
will  be  high,  and  possibly  preclude  its  use. 

In  fibres  of  low  yield  and  consuming  a  large  amount  of 
chemicals,  the  cost  of  chemical  treatment  per  ton  of  finished  stuff 
is  often  so  high  as  to  condemn  the  material  for  industrial  use,  no 
matter  even  if  the  resulting  cellulose  is  of  excellent  quality,  and 
the  raw  material  had  for  the  asking. 

Such  considerations  as  these  must  be  weighed  with  the 
greatest  care  in  estimating  the  value  of  of  any  material  for  the 
purposes  of  paper  manufacture. 

Por  the  examination  of  rags  I  would  refer  you  to  my 
publication  in  the  Chemical  News,  in  which  I  gave  the  mode 
of  determining  the  yield  on  boiling,  and  the  amount  of  chemicals 
used  up.  If  you  require  to  know  the  loss  of  any  quality  of  rag 
that  happens  to  be  under  treatment  in  the  paper  mill,  it  is  a  very 
simple  matter  to  take  say  10  lbs.  of  rags  and  tie  them  up  in  a  bag 
of  open  material,  such  as  cheese  cloth,  and  throw  the  same  into 
the  boiling  of  the  same  rags.  When  the  boiler  is  discharged 


18 


the  bag  of  rags  is  fished  out,  and  after  washing  is  carefully  air- 
dried  and  weighed.  The  yield  can  easily  be  calculated.  Many 
rags  contain  a  lot  of  dressing.  The  mineral  matter  in  such 
dressing  can  be  determined  by  burning  off  an  average  sample, 
and  the  total  amount  of  dressing  is  easily  removed  by  washing  in 
hot  water. 

As  new  rags  of  this  description  often  contain  as  much  as  60 
per  cent,  of  dressing,  it  is  a  very  important  matter  to  determine 
what  the  loss  is.  The  most  practical  way  of  estimating  the  value 
of  any  particular  class  of  rags  is  to  take  a  bale  of  rags  and  have 
them  sorted  and  cut  into  various  qualities,  weighing  each,  and 
as  the  price  of  each  quality  is  known  in  the  mill,  the  value  of  the 
original  rags  can  be  calculated  therefrom. 

If  time  had  permitted  I  should  like  to  have  referred  you  to 
many  other  points  in  connection  with  this  subject,  such  as  the 
valuation  of  flax  waste,  cotton  hulls,  and  other  products,  but 
possibly  there  will  be  an  opportunity  of  referring  to  these  and 
other  matters  in  some  future  lecture. 


Literature. — Indian  and  Colonial  Exhibition  Reports.  (Wm.Clowes  &  Sons,  Ltd. 
1887.)  Report  on  Indian  Fibres  and  Fibrous  Substances.  (E.  &  F.  N.  Spon.  1887.) 
Cellulose.  (Cross,  Bevan,  and  Beadle.  Longmans,  Green,  &  Co.  1895.)  Beadle  :  Paper 
and  Pulp,  October  15th,  1901.  Beadle:  The  Systematic  Treatment  of  Rags,  Chemical 
INews,  1901. 


LECTURE  II. 


ART  PAPERS  AS  APPLIED  TO  PROCESS 
PRINTING. 

Art — Imitation  art — Nature  of  surface — Nature  of  fibres — Minerals  used — 
Preparation  and  application  of  coating  —  Casein — Gelatine  —  Test  for 
Coating — Preparation  of  process  blocks — Chemical  and  physical  examination 
— Nature  and  utility  of  coated  surface. 


The  so-called  “  art  ”  or  imitation  art  papers  liave  come  into 
vogue  very  much  during  the  last  few  years. 

They  have  rendered  so-called  process  printing  not  only  possible, 
but  have  been  largely  the  means  of  reducing  it  to  a  tine  art. 
Although  such  papers  are  by  no  means  artistic,  either  in  appear¬ 
ance  or  composition,  they  have  through  their  very  nature  become 
the  means  or  medium  of  rendering  art  by  mechanical  processes. 
It  must  be  remembered  that  the  surface  of  an  enamelled  paper 
is  not  paper  at  all.  Paper  must  consist  of  fibres,  and  ordinary 
paper  which  is  not  coated  partakes  not  only  of  the  chemical 
nature  of  cellulose,  but  of  its  physical  nature  also.  The  physical 
structure  of  the  cellulose  fibres  renders  it  difficult  to  impart  to 
paper  of  any  description  the  fine  tones  and  half-tones  of  process 
printing.  Any  spreading  or  diffusion  of  the  ink  would  naturally 
tend  to  travel  along  the  tubes  of  the  fibres,  but  with  a  coated 
paper,  although  there  is  great  power  of  absorption,  there  is  no 
tendency  to  diffuse  in  one  direction  more  than  in  any  other. 
On  the  other  hand,  when  the  paper  is  enamelled,  the  surface 
alters  its  character  entirely,  and  partakes  of  the  nature  of 
whatever  mineral  matter  the  enamel  contains,  the  paper  itself 
playing  a  subordinate  part.  Assume  that  the  basis  of  the 
coating  consists  largely  of  clay.  In  the  process  of  printing 
the  ink  does  not  come  in  contact  with  the  fibres  at  all,  but  merely 
in  contact  with  the  enamelled  surface  of  the  paper.  In  other 
words,  it  comes  in  contact  with  a  uniform  smooth  surface  of 
clay  held  together  by  means  of  some  adhesive  material.  The  ink 
is  absorbed  by  this  surface,  and  has  no  tendency  to  spread,  as  it 
might  do  should  it  come  in  contact  with  the  fibres  of  the  paper. 
But  the  main  difference  between  the  enamelled  surface  and 


20 


the  unenamelled  surface  of  the  paper  is  the  degree  of 
smoothness. 

Particles  of  clay  are  infinitely  smaller  and  finer  than  the 
fibres  composing  the  paper,  and  consequently  present  a  much 
more  uniform  and  compact  surface  than  fibres  would  do  if 
uncovered  with  enamel. 

Even  with  a  great  deal  of  glazing  with  calenders  it  is  im¬ 
possible  to  give  to  the  surface  of  an  uncoated  paper  the  same 
regularity  as  to  the  surface  of  an  art  paper.  If  you  could 
very  much  magnify  an  art  paper  w'hen  viewed  in  sections,  you 
would  notice  the  surface  of  the  paper  proper,  i.e.,  the  waterleaf, 
has  an  undulating  or  wavy  appearance,  whereas  the  surface  of 
the  enamel,  although  it  might  appear  granular  and  show  the 
individual  particles  of  mineral,  would  present  a  fairly  flat  and 
compact  surface. 

I  will  endeavour  to  give  you  a  brief  description  of  the 
preparation  of  the  paper,  together  with  preparation  and  use  of 
the  enamel  for  the  manufacture  of  an  art  paper  : — 

An  art  paper,  in  order  to  stand  wear  and  tear,  must  be 
made  of  good  material,  but  if  it  is  not  required  to  be  strong, 
and  if  it  admits  of  being  heavily  coated,  the  fibrous  material  is 
not  of  so  much  consequence;  in  fact,  I  have  known  common 
papers  heavily  loaded  with  enamel  and  containing  as  much  as  30 
per  cent,  of  mineral  matter  to  consist  largely  of  mechanical 
wood.  The  enamelled  surface  may  be  made  to  cover  a  multitude 
of  sins.  When  such  papers  are  moistened  and  rubbed,  the 
whole  of  the  surface,  together  with  the  printed  matter,  comes 
away,  and  it  can  be  readily  seen,  when  the  enamel  is  removed, 
that  the  paper  itself  is  made  of  very  common  material. 

Such  paper  is  very  deceptive  material  for  any  publication 
which  may  be  required  for  reference.  If  exposed  to  the  daylight 
it  discolours  and  becomes  rotten,  and  easily  pulverises.  These 
papers  are  deceptive  because  the  thickness  of  the  enamel  hides 
their  imperfections.  AVhen  an  imitation  art  paper  of  this 
description  is  used  for  the  purpose  of  publications,  it  will  be 
noticed,  on  turning  over  the  pages,  that  the  paper  has  quite 
a  leathery  feel  and  sound,  although  the  paper  is  easily  torn. 
The  mineral  contained  in  the  enamel  will  largely  influence  the 
character  of  surface  as  regards  feel  and  general  physical 
qualities. 

Such  papers  are  also  very  fatiguing  to  the  eye  if  the 
printed  matter  is  read  in  a  bright  light,  especially  when  the 
light  strikes  at  certain  angles,  but  they  possess  in  a  very  high 


21 


degree  tlie  power  of  receiving  half-tone  impressions,  tor  which  they 
are  so  admirably  adapted.  This  is  their  great  redeeming  feature. 

The  following  is  a  description  of  the  method  employed  in 
the  coating  of  an  art  paper,  as  described  by  “  A  Header  ”  in 
the  columns  of  Paper  akd  Pulp,  January  1st,  1902  : 

“The  coating  machine  consists  of  a  cylinder  or  drum  varying  from 
three  to  four  feet  in  diameter,  which  acts  as  a  support  to  the  paper  as 
well  as  a  carrier  when  under  the  influence  of  the  brushes.  The  colour 
box  is  made  of  copper,  and  is  arranged  so  that  heat  may  be  applied,  in 
order  to  keep  the  colour  always  at  the  same  temperature.  The  coating  is 
applied  to  the  paper  by  means  of  a  vertically-running  felt  which  does  not 
pass  through  the  colour  box,  but  to  which  the  colour  is  transferred  by 
means  of  a  copper  roll  running  in  the  box,  the  amount  of  coating  so 
transferred  being  regulated  by  the  degree  of  pressure  of  the  felt  against 
a  parallel  roll  between  which  the  paper  passes.  The  distribution  of  the 
coating  is  effected  bv  means  of  five  or  seven  brushes,  the  bristles  being 
so  selected  in  quality  as  to  become  softer  and  softer  in  succession.  The 
brushes  work  with  different  motions,  some  being  stationary,  others  moving 
to  and  fro  sideways,  the  latter  motion  being  supplied  by  cranks  all  fixed 
on  one  shaft  and  driven  by  belt.  At  the  end  of  the  coating  machine  is 
generally  fixed  a  pneumatic  suction  table  on  which  the  now  coated  paper 
passes.  This  table  acts  as  a  drawer,  and  prevents  the  paper  slipping  on 
the  drum,  after  which  it  passes  on  to  the  drying  apparatus.  This  apparatus 
consists  of  a  system  of  endless  chains,  on  which  are  carried  sticks,  the 
paper  hanging  from  these  sticks  in  loop  torm,  and  is  subjected  to  a  tempera¬ 
ture  varying  from  80  degrees  to  90  degrees  Fahr.  If  the  drying  room  is 
not  long  enough  this  apparatus  is  fitted  with  a  turntable,  which  takes  the 
sticks,  describes  with  them  a  semi-circle,  puts  them  in  turn  on  to 
returning  chains  and  finally  delivers  them  into  a  self-taking  and  removing 
apparatus,  the  coated  paper  passing  on  to  the  reeling  machine.  After  tie 
reel  is  of  sufficient  size  it  is  taken  off,  and  in  the  case  of  a  high  class  ‘art, 
is  recoated  on  the  opposite  side.  As  a  rule,  part  of  the  day  is  devoted 
to  coating  one  side,  and  the  rest  the  opposite  side.  The  coating  or  enamel 
consists  of  a  mixture  of  satin  white,  blanc  fixe,  enamel  or  china  clay,  used  in 
varying  proportions  according  to  the  desired  finish.  Gelatine  is  added 
to  the  mixture  to  size,  in  order  tc  prevent  the  coat  from  lifting  when 
printed.  The  speed  of  coating  varies  according  to  the  width  of  reel  coated, 
but  an  average  may  he  taken  at  80  to  120  feet,  and  in  some  cases  at  the 
speed  of  140  feet.”  . 

Blanc  fixe  is  also  known  as  permanent  white,  or  chemically 
as  barium  sulphate.  It  is  prepared  artificially,  and  is  much 
preferred  to  the  natural  ground  mineral,  as  the  latter  is  crystal¬ 
lised  and  has  very  little  covering  power  or  “body.” 

Satin  white  is  a  mixture  of  hydrated  alumina  and  calcium  or 
barium  sulphate. 

You  will  find  a  good  deal  of  information  on  this  subject  on 
reading  through  Paper  and  Pulp. 

The  two  chief  materials  used  as  adhesive  materials  are 
gelatine  and  casein;  the  latter  has  come  more  to  the  fore  of 


22 


recent  years,  although  gelatine  appears  to  possess  certain  advan¬ 
tages  which  casein  does  not.  It  is  difficult  to  find  information 
on  this  subject  in  any  of  the  text-hooks,  but  here  and  there  one 
finds  fragmentary  references  in  our  scientific  literature.  For 
much  of  the  following  information,  in  regard  to  the  use  of  casein, 
I  am  indebted  to  Messrs.  Spicer  Brothers,  Ltd. 

Insoluble  casein,  as  you  may  know,  requires  an  alkali  to 
dissolve  it.  The  alkalies  generally  used  in  practice  are  either 
ammonia,  soda,  or  borax.  Which  alkali  should  be  used,  or 
whether  a  combination  of  alkalies  should  be  used,  depends  upon 
whether  china  clay,  blanc  fixe,  satin  white,  or  other  material  forms 
the  basis  of  the  enamel. 

The  user  must  bear  in  mind  that  once  having  got  his  solution 
the  rest  of  the  work  is  practically  the  same  as  with  glue. 
It  may  be  necessary  to  neutralise  if  the  blanc  fixe  or  other 
material  is  of  an  acid  nature.  Some  colours  used  in  mills  are 
so  acid,  that  to  add  the  casein  solution  to  them  straight  away 
would  have  resulted  in  nothing  but  a  curdled  mass,  impossible 
to  use  for  coating.  When,  however,  the  mixing  is  neutralised  the 
colours  should  give  no  trouble  in  the  working.  There  are  many 
mills  in  this  country  now  using  the  casein,  as  it  gives  a  clear 
solution  and  preserves  special  features  which  render  it  of  service 
for  certain  work.  Casein  has  to  a  certain  extent  been  used  for 
engine  sizing,  particularly  in  the  United  States,  but  not  to  any 
extent,  so  far  as  I  can  ascertain,  in  this  country. 

For  the  purpose  of  making  up  the  enamel  the  insoluble  casein 
is  treated  in  the  following  manner  : — 

As  above  stated,  the  casein  as  received  is  insoluble,  and 
has  been  rendered  soluble  by  the  addition  of  either  ammonia, 
borax,  or  soda. 

To  every  pound  of  dry  casein  to  be  used  add  three  pints  of 
cold  water  (if  very  thin  coats  are  required,  four  pints),  and  stir 
the  casein  in  the  cold  water  so  that  no  lumps  are  left.  Soak  for 
ten  minutes  or  so  and  then  apply  heat  in  the  usual  way,  either 
by  turning  in  live  steam  or  by  heating  in  a  steam-jacketed  pan. 
The  mass  should  be  stirred  while  heating,  the  same  as  with  glue. 
When  the  temperature  is,  say,  100°  Fahr.  the  alkali  may  be 
added ;  and  when  the  temperature  has  reached  140°  or  150° 
Fahr.  the  heat  should  be  turned  off  and  the  size  agitated  until  a 
perfectly  smooth  solution  without  any  sediment  is  obtained.  It  is 
of  advantage  to  dissolve  as  slowly  as  possible,  as  the  size  will  be 
stronger. 


23 


If  ammonia  be  the  alkali  used  to  dissolve  the  casein,  one 
ounce  of  ammonia  26  per  cent,  (or  .901  specific  gravity)  should 
be  sufficient  to  dissolve  each  pound  of  casein  used.  If  the 
ammonia  should  have  lost  any  of  its  strength  due  to  evaporation 
more  will  be  needed. 

For  using  casein  with  colours  borax  is  the  best  alkali  to 
use,  as  it  does  not  affect  the  colours  nor  change  the  shades.  20 
per  cent,  to  25  per  cent,  of  borax  is  ample  to  dissolve  the  casein, 
and  the  borax  should  be  dissolved  in  part  of  the  water  to  be  used 
for  mixing  with  the  casein. 

For  white,  such  as  china  clay  or  blanc  fixe,  the  alkali  may 
be  monohydrate  of  soda  (Solvay  process)  or  crystal  carbonate  of 
soda,  the  proportion  of  monohydrate  to  be  used  being  12  per 
cent.,  and  the  proportion  of  crystal  carbonate  15  per  cent. 
The  soda  should  be  dissolved  in  a  portion  of  the  water  used  to 
mix  with  the  casein. 

If  it  is  wished  to  use  soda  and  borax  together,  take  8  per 
cent,  of  either  monohydrate  or  crystal  carbonate  of  soda  and  10 
per  cent,  borax :  this  solvent  can  be  used  with  clay,  blanc  fixe,  or 
colours. 

For  satin  white  take  15  per  cent,  of  monohydrate  of  soda 
or  18  per  cent,  of  crystal  carbonate  of  soda,  dissolving  whichever 
is  used  in  some  of  the  water  used  for  mixing  the  casein. 

It  must  be  borne  in  mind  that  it  is  always  necessary  to 
have  the  size  on  the  alkaline  side,  to  get  and  keep  the  casein 
in  solution. 

There  are  difficulties  to  be  overcome  in  regard  to  the  addition 
of  colour  both  in  the  use  of  glue  and  casein.  The  following 
method  of  testing  whether  the  coating  is  done  in  a  proper  manner 
is  given  in  the  Papier  Zeitung,  as  abstracted  in  the  Journal  of 
the  Society  of  Chemical  Industry 

“For  the  examination  as  to  the  value  of  the  coat  there  are 
three  tests :  (1)  The  moistened  thumb  is  pressed  against  the 
paper  and  removed.  If  any  of  the  colour,  &c.,  adheres  to  the 
thumb,  then  the  paper  is  badly  coated.  (2)  A  piece  of  the  folded 
paper  is  rubbed  between  the  fingers,  and  notice  is  taken  as  to 
whether  any  of  the  coat,  and  how  much,  has  come  off.  The 
most  reliable  is — (3)-  A  strip  of  uncoated  sized  paper  covered 
with  the  best  glue  is  moistened  and  pasted  on  to  the  coated 
paper  which  is  to  be  examined.  After  drying,  an  attempt  is  made 
to  separate  the  pieces  of  paper.  According  to  whether  the 
coat  of  colour  adheres  to  the  paste  or  not,  separation  takes 


24 


place  either  along  the  coated  surface  or  the  fibres  are  torn  away. 
If  the  former,  the  coating  is  bad;  if  the  latter,  it  is  good.” 

It  must  be  borne  in  mind  that  the  above  test  could  not 
be  laid  down  as  applying  to  all  coated  papers.  Some  are 
required  to  stand  better  than  others.  In  any  case,  however,  the 
surface  should  be  such  as  not  to  lift  on  the  blocks.  The 
condition  of  the  enamel  is  largely  dependent  upon  the  propor¬ 
tion  of  adhesive  material  to  mineral  matter.  Naturally  the  paper- 
maker  desires  to  get  the  proper  effect  with  the  least  quantity  of 
adhesive.  Formaline  is  often  used  to  render  the  casein  insoluble, 
so  that  the  coating  may  be  impervious  to  moisture. 

The  following  particulars  in  regard  to  Schmidt’s  American 
Patent  are  interesting  in  this  connection,  as  given  in  the  Journal 
of  the  Society  of  Chemical  Industry  : — 

“  When  a  5  per  cent,  solution  of  soda-casein  is  mixed  with 
formaldehyde,  no  coagulation  takes  place,  the  solution  remains 
clear  and  liquid  for  a  long  time.  But  when  such  a  mixture  is 
spread  out  on  glass  or  paper  and  allowed  to  dry,  a  transparent 
film  of  casein  is  formed  which  is  completely  insoluble  in  water. 
Films  of  casein  so  treated  may  be  distinguished  from  ordinary 
films  in  the  following  manner.  The  films  are  carefully  removed 
from  their  backings  and  placed  in  water  to  which  a  couple  of 
drops  of  methylene  blue  have  been  added.  On  warming,  the  film 
which  has  not  been  treated  with  formaldehyde  is  dyed  a 
pale  blue,  whilst  the  formaldehyde  film  assumes  a  dark  blue 
colour.  A  solution  of  casein  in  ammonia  behaves  in  a  similar 
manner,  but  if  large  quantities  of  formaldehyde  be  added,  a 
precipitate  is  formed.  The  following  proportions  are  cited: 
100  grammes  of  casein  and  1.5  grammes  of  caustic  soda  are 
dissolved  in  a  litre  of  water,  to  which  are  added  about  15 
grammes  of  a  40  per  cent,  solution  of  formaldehyde,  or  100 
grammes  of  casein  and  10  c.c.  of  a  10  per  cent,  solution  of 
ammonia  are  dissolved  in  two  litres  of  water,  to  which  are  added 
about  30  grammes  of  a  40  per  cent,  solution  of  formaldehyde. 
Either  of  these  gives  insoluble  films  on  drying,  which  may  be  used 
for  photography,  surgical  bandages,  paper-coating,  &c.” 

In  order  to  appreciate  in  what  way  enamelled  papers  are  of 
service  to  the  printing  trade,  it  is  necessary  to  know  something 
about  the  various  methods  for  the  mechanical  reproduction  of 
photographs  aDd  process  blocks.  It  is  impossible  to  refer  in 
detail  to  more  than  one  process.  The  following  description 
from  Mr.  J.  D.  Geddes’  Cantor  Lectures  on  “  Photography  as 


.applied  to  Illustration  Printing,”  recently  published  in  the 
Society  of  Arts  Journal,  gives  a  very  lucid  description  of 
Jhe  processes  involved.  This  will  help  you  to  realise  the 
difficulties  with  which  the  papermaker  has  to  contend  in  the 
production  of  paper  which  will  prove  itself  suitable  for  the 
work.  It  can  be  readily  understood  on  reading  this  through 
that  the  surface  of  the  paper  must  be  extremely  uniform  and 
free  from  all  irregularities.  In  fact,  an  ideal  art  paper  should 
have  an  absolutely  plain  surface,  so  that  when  viewed  under  the 
microscope  it  should  not  show  any  ups  and  downs  at  all : — 

“  Preparation  of  the  Diamond-Rcled  Screens  of 
Mr.  Max  Levy,  of  Philadelphia. 

“A  sheet  of  the  finest  plate  glass  is  selected,  and  is  coated  with  a 
'varnish  composed  of  asphalt  and  wax.  The  coated  glass  is  placed  on  the 
■bed  of  an  automatic  ruling  machine  of  extremely  accurate  construction, 
and  capable  of  ruling  lines  of  any  degree  of  fineness  up  to  500  to  the  inch. 
The  cutter  of  the  machine  is  diamond-pointed,  and  gauged  to  cut  lines 
•of  any  desired  width.  The  lines  are  ruled  diagonally  at  45^  across 
the  glass,  and  the  Dumber  to  the  inch  varies  according  to  the  kind  of 
'work  for  which  the  screen  is  required.  For  newspaper  printing  the  lines 
may  be  50  or  00  to  the  inch  ;  for  commercial  and  catalogue  printing, 
100  to  130 ;  and  for  finer  magazine  or  book  illustration,  150  to  200  to  the 
•inch.  When  the  ruling  of  the  glass  is  completed,  the  ruled  surface  is 
subjected  to  the  action  of  the  hydrofluoric  acid,  which  eats  into  or  etches 
the  lines  laid  bare  by  the  diamond,  and  forms  a  channel  which  is  filled 
up  with  opaqae  pigment.  This  enamel  is  baked  in  the  lines  in  an  oven,  and 
Then  ihe  surface  is  carefully  polished  until  the  lines  are  perfectly  level 
and  the  spaces  represented  by  clear  glass  are  bright  ar.d  transparent. 

“  Two  of  these  ruled  glasses  are  required  for  each  screen,  laid  together 
with  the  lines  crossing  at  right  angles,  and  cemented  with  Canada  balsam. 
As  may  be  imagined,  the  screen  gratiDgs  are  somewhat  expensive  :  a  piece 
measuring  12  inches  by  10  inches  of  175  lines  costs  about  £25,  whilst  large 
■screens  of  24  by  18  are  charged  at  £100  or  more.  I  am  glad  to  state  that 
we  have  now  an  English  firm  (Messrs.  J.  E.  Johnson  &  Co.)  who  rule 
these  screens  excellently,  indeed,  there  is  little  to  choose  between  this  work 
and  the  best  American,  which  is  a  comforting  thing  to  say  in  these  days  when 
it  is  the  habit  of  the  ever-present  pessimist  to  decry  everything  that  is 
English  and  all  that  the  Britisher  does. 

“  To  produce  a  ha.lf-tone  block  from  a  picture,  wash  drawing,  or 
photograph,  this  ruled  grating  is  placed  in  front  of  the  sensitive  plate,  but 
not  in  contact  with  it.  The  screen  distance  from  ihe  sensitive  plate  is  a 
j)oint  of  importance  in  making  the  negative,  and  the  skilful  operator  has 
to  determine  this  distance  according  to  his  expeiience,  and  to  tbe  character 
of  the  subject  which  is  to  be  photographed.  If  it  is  placed  too  close  the 
resulting  negative  will  present  what  is  known  as  a  gridiron  appearance, 
if  it  is  too  far  away,  the  dotting  will  be  too  close  in  the  lights  and  too  small 
in  the  shadows.  You  will  understand  how  necessary  it  is  to  keep  a  nice 
balance  in  this  matter  in  the  case  of  a  picture  which  is  built  up  entirely  of 
.an  infinity  of  dots,  shadows  being  represented  by  grouping  of  dots  close 


26 


together,  with  smallest  of  spaces  between  middle  and  light  tones  by  dots 
of  different  graduations  in  sue,  and  the  highest  lights  of  pin-point  dots 
only.  Everything  is  represented  by  dots,  yet  they  are  so  accurately  graded 
in  relation  to  the  light  and  shade  of  the  original,  that  the  eye  does  not 
detect  them,  unless  examined  closely,  and  the  half-tone  picture  appears 
as  a  practical  fac-simile  of  the  original  from  which  it  was  photographed. 

“The  method  of  printing  half-tone  negatives  on  metal  is  similar  in 
most  respects  to  that  described  for  line  blocks  on  zinc,  with  this  difference, 
that  most  half-tone  blocks  are  now  etched  on  copper,  and  the  sensitising 
solution  generally  employed  for  this  metal  is  a  compound  of  fish  glue, 
albumen,  chromic  acid,  water,  and  bichromate  of  ammonia.  The  copper 
is  carefully  cleaned  with  Tripoli  powder  and  washed,  the  sensitising 
solution  is  then  flowed  over  it  twice  or  three  times  and  placed  on  a 
revolving  table,  where  it  is  rapidly  whirled  in  order  to  spread  the  coating 
thinly  and  evenly  over  the  whole  surface;  the  coating  is  then  dried  by 
gentle  heat  in  a  yellow  lighted  room,  and  the  plate  is  now  ready  for 
exposure.  Under  the  half-tone  negative,  three  to  ten  minutes’  exposure 
to  an  electric  arc  light  completes  the  printing,  when  the  plate  is 
removed  to  a  bath  containing  cold  water,  and  soaked  and  washed  under 
a  spray  of  water  until  the  unacted-upon  compound  is  dissolved  out,  an 
operation  occupying  five  or  six  minutes.  The  imagery  on  the  metal  at  this 
stagt:  is  almost  invisible.  In  order  to  enable  an  examination  of  the  film 
to  be  made,  the  plate  is  dipped  into  a  solution  of  methyl  violet,  which 
dye  immediately  stains  the  film,  and  brings  the  picture  into  view. 
If  all  has  gone  well,  the  surface  is  dried  either  by  flowing  it  with  methyl¬ 
ated  alcohol  or  gentle  heat.  The  next  operation  has  an  important  effect, 
namely,  a  hardening  of  the  delicate  glue  picture  into  a  substance  resembling 
enamel,  and  this  gives  the  method  its  name — ‘the  enameline  process.’ 

“The  plate  is  simply  heated  to  a  high  temperature  over  the  flame  of 
a  large  ‘  Bunsen  ’  burner.  During  the  progress  of  this  ‘  burning  in  ’  or 
enamelling,  the  image  changes  curiously  ;  the  blue  picture  gets  pale,  then 
grey,  and  eventually  vanishes  entirely'.  After  a  few  seconds,  as  the  plate 
gets  hotter,  the  image  appears  as  a  faint  brown  and  gradually  increases  in 
strength  until  it  fully  attains  a  rich  chestnut  brown  tint,  when  the  heat 
must  be  withdrawn,  and  the  plate  is  cooled  off.  The  plate  has  now  a 
picture  fixed  upon  it,  which  is  formed  of  a  strong,  hard,  impermeable 
coating  of  enamel,  and  which  will  bear  any  reasonable  amount  of  etching 
without  further  protection.  The  etching  bath  is  made  up  of  neutral 
perchloride  of  iron  dissolved  in  water  and  of  a  strength  which  registers  35 
degrees  with  a  Baumh’s  hydrometer.  The  plate  is  first  subjected  to  a 
general  etching  all  over  the  plate  sufficient  to  give  the  block  a  printing 
depth,  that  is,  to  etch  away  the  spaces  round  the  dots  forming  the  picture 
so  that  the  plate  may  be  inked  over  with  a  printer's  roller  charged  with 
ink,  and  a  first  proof  of  the  photo-etched  picture  pulled  in  the  press.  In 
most  plates  made  by  this  process  a  further  and  local  etching  must  be  per¬ 
formed.  The  dulling  of  the  general  effect  caused  by  the  interposition  of 
the  necessary  screen  grating  has  to  be  removed  as  far  as  possible,  and 
this  is  done  by  artists  who  are  specially  trained  for  the  work.  The 
parts  of  the  picture  which  are  in  shadow  and  are  usually  correctly 
rendered  by  a  properly  exposed  negative,  are  covered  over  with  varnish 
and  the  next  tones  are  etched  again,  and  these  tones  are  covered  up  and 
the  high  lights  are  treated  until  the  resulting  picture,  when  proofed, 
correctly  represents  the  original.  The  plates  are  then  trimmed  by 


27 


engravers,  bevelled  to  admit  of  being  riveted  to  the  wood  mounts,  and 
are  mounted  type-high  for  use  in  the  printing  press.’’ 

Other  Processes,  as  Described  in  “  The  Story  op  Photography,” 
by  Alfred  T.  Story'. 

“The  best  known  in  England  is  the  Meisenbach  process,  which,  after 
having  been  worked  by  Messrs.  Bullock  and  Swan  for  a  number  of  years, 
was  patented  by  Meisenbach  in  1882.  The  process  is  thus  described  : — A 
transparent  plate  is  etched  or  stippled  in  parallel  lines.  A  transparent 
positive  is  made  of  the  object,  the  two  plates  are  joined,  preferably  face 
to  face,  and  from  the  combined  plates  a  definite  negative  is  photographed 
in  the  ordinary  way.  In  order  to  cross-hatch  and  break  the  lines  of  the 
shading,  the  hatched  or  stippled  plate  may  be  shifted  once  or  twice  during 
the  production  of  the  negative.  The  photographic  negative  thus  obtained 
may  be  applied  either  directly  to  a  zinc  plate,  or  a  lithographic  transfer 
may  first  be  made  in  the  usual  manner,  and  the  plate  subsequently  bitten 
by  acid  to  form  a  block  in  relief. 

“The  Ives  process  is  a  very  original  one  in  so  far  as  the  reproduction 
of  half-tone  is  concerned,  and  its  excellent  results  may  be  seen  in  many  of 
the  American  magazines,  which  until  very  recently  left  our  English  periodi¬ 
cals  far  in  the  shade  as  regards  their  illustrations.  Of  late,  however, 
the  English  magazines  have  been  gaining  ground  very  rapidly. 

“  In  the  finer  and  more  artistic  forms  of  photogravure  England  seems  to 
have  been  left  almost  entirely  behind — as  in  so  many  other  departments 
where  exceptional  knowledge  of  technique  is  required — by  the  French  and 
the  Germans,  nearly  all  the  best  reproductions  of  large  pictures  by  photo¬ 
gravure  being  done  at  Baris  or  Berlin.” 

The  following  are  the  results  of  physical  tests  on  some  art 
papers  which  I  undertook  for  this  lecture.  They  comprise  the 
following  publications  :  The  Graphic,  The  Papermaker,  Supple¬ 
ment  to  the  Graphic,  The  Sphere,  Black  and  White,  The 
Sketch,  Illustrated  Sporting  and  Dramatic  News: — 


Ashes  oe  Art  Papers'  after  the  Removal  of  Enamel. 


No. 

86 

87 

88 

89 

90 

91 
85 


Percentage  of  Ash. 
22.8 
16  2 

19.6 
15.8 

22.7 
29.0 
19.3 


The  results  as  shown  in  these  tables  are  arrived  at  by 
means  of  a  special  instrument  which  I  have  had  made,  which, 
together  with  the  use  of  a  micrometer  gauge,  has  enabled  me  to 
work  out,  not  only  the  weight  of  a  given  volume  of  paper 
expressed  in  grammes  per  c.c.,  but  also  the  weight  of  the  fibre 


* 


The  Results  of  Physical  Tests  on  some  Art  Papers. 


28 


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29 


and  ash  in  grammes  per  c.c.  From  these  results  it  is  possible 
by  a  process  of  calculation,  which  I  have  already  referred  to  in  my 
answer  to  last  years  City  and  Guilds  examination  questions,  to 
calculate  the  actual  volume  percentages.  Thus,  if  we  had,  for  the 
sake  of  argument,  a  cubic  inch  of  paper,  by  cutting  pieces  of  a 
square  inch  area  and  laying  them  one  on  top  of  each  other  until 
they,  when  pressed  down,  measured  an  inch  in  height,  we  could 
say  what  proportion  of  this  area  was  occupied  by  the  cellulose 
or  fibre,  what  proportion  was  occupied  by  the  clay,  and  what 
proportion  by  the  air  space  or  interstices  of  the  paper.  I  have 
undertaken  these  few  results  purposely  for  use  in  this  lecture. 
My  colleagues  and  I  are  engaged  in  results  of  this  kind  in  different 
classes  of  paper,  on  about  90  specimens,  with  a  view  of  deter¬ 
mining  whether  we  can  devise  some  better  modes  of  testing 
and  classification  than  is  at  present  in  vogue  at  the  Charlottenburg 
Government  testing  station.  The  results  of  these  investigations 
will  be  published  in  due  course  when  they  are  completed.*  You 
will  notice  that  the  air  space  or  interstices  of  these  papers  runs 
from  about  20  to  30  per  cent.  A  shows  the  breaking  strain 
when  pulled  in  the  direction  of  the  web,  and  B  when  pulled  across 
the  web,  in  lbs.  on  a  one-inch  width.  This  is  calculated  into 
grammes,  and  finally  expressed  in  li  weight  length,’  as  is  done 
in  Germany.  The  ash  of  these  papers  varies  from  16  to  over  30 
per  cent.,  and  the  heaviest  loaded  paper  shows  the  least  strength 
and  the  least  loaded  is  nearly  the  strongest.  From  these  tables 
you  can  arrive  at  useful  data,  such  as  the  weight  per  cubic  foot, 
useful  for  the  purposes  of  stocktaking,  and  show  the  relative 
amount  of  bulking,  useful  to  printers  in  arriving  at  the  weight 
which  a  given  book  will  require  as  well  as  its  thickness.  The  discs 
are  punched  out  of  such  a  size  that  the  thickness  of  ten  discs  in 
mm.  gives  the  volume  in  c.c. 

As  regards  the  amount  of  enamel  used  I  should  like  to 
point  out  that  this  does  not  bear  any  direct  relation  to  the  weight 
of  paper  coated.  For  a  given  purpose  a  certain  thickness  of 
enamel  would  be  required.  It  is  a  question  therefore  of  area, 
not  of  weight.  For  every  ream  of  demy  we  might  reckon  upon 
an  addition  to  the  weight  per  ream  of  10  lbs.  If  the  uncoated 
paper  weighed  20  lbs.  to  the  ream,  the  coated  would  weigh  30.  If 
60  lbs.  the  coated  would  weigh  70.  The  paper  is  rolled  twice  and 
must  be  rolled  sufficiently  on  the  under  side  to  obliterate  the  wire 


*  Since  this  lecture  was  delivered  the  results  in  question  have  been  published  in 
pamphlet  form \see  “An  Essay  towards  Establishing  a  Normal  System  of  Paper  Testing, "by- 
Cross,  Sevan,  Beadle,  and  Sindall.  Wood  Pulp,  Ltd. 


30 


mark.  It  should  also  be  coated  more  heavily  on  the  under  side. 
The  coating  should  be  conducted  in  such  a  manner  as  to  ensure 
absolute  evenness  and  there  must  be  no  waviness.  When  paper  is 
used  tor  chromo-lithography,  the  enamelled  surface  should  be 
perfectly  neutral  to  prevent  any  action  upon  the  colours.  When 
casein  is  used  and  it  is  desired  to  obtain  a  neutral  coating,  I 
should  recommend  the  use  of  ammonia  as  the  alkali  for  rendering 
the  casein  soluble,  and  I  should  consider  that  this  mixture  in 
conjunction  with  formalin  would  produce  the  most  water-resistant 
and  insoluble  surface. 

The  difficulty  urged  against  casein  is  the  uncertainty  of  its 
behaviour  and  its  liability  to  give  a  brittle  surface.  This  may 
largely  be  due  to  want  of  skill  in  its  manipulation.  The  glue  or 
gelatine  used  as  the  adhesive  material  is  not  that  ordinarily  used 
for  the  tub-sizing  of  papers.  Tub-sizing  gelatine  is  required  of  a 
different  nature  to  gelatine  for  enamelling  purposes,  and  the 
one  cannot  be  used  for  the  other  with  advantage.  The  amount 
of  gelatine  (or  casein)  in  relation  to  the  amount  of  mineral 
matter  as  well  as  the  dilution  of  the  paste  must  be  adjusted  to 
suit  requirements.  This  is  only  arrived  at  as  a  matter  of 
experience.  If  too  little  gelatine  is  used  the  surface  will  rub  off 
and  lift  in  contact  with  the  blocks  ;  if  too  much  is  used  the  surface 
is  of  a  harsh  nature.  The  enameller  desires,  of  course,  to  get  the 
result  with  the  least  quantity  of  gelatine  or  casein  on  account  of 
the  expense  of  these  products.  In  course  of  time  the  enamelled 
surface  is  often  acted  on  by  contact  with  air  and  moisture  and 
bacteria,  the  result  being  that  the  adhesive  material  is  destroyed, 
leaving  the  clay  easily  removable  by  rubbing. '  It  is  hardly 
probable  that  an  enamelled  paper  will  last  many  years,  more 
especially  in  a  warm  damp  climate.  For  chromo-lithography 
absolute  freedom  from  stretch  or  expansion  in  contact  with  the 
damp  cylinder  is  an  essential  quality,  otherwise  the  register  will 
not  be  true.  Formalin  acts  not  only  as  a  substance  to  render 
the  adhesive  material  insoluble,  but  is  also  a  preservative.  An 
art  paper,  of  course,  is  absolutely  useless  for  writing  upon.  The 
ink  diffuses  in  all  directions  and  soaks  through  the  enamel. 
Printer’s  ink  as  you  know  is  a  mixture  of  drying  oil  and  pigments. 
The  printer’s  block  merely  imparts  to  the  surface  of  the  enamel 
an  extremely  thin  film  of  ink  which  is  rendered  insoluble  by 
oxidation  by  contact  with  the  air,  but  cannot  be  said  to  dry  in 
the  ordinary  sense  of  the  term.  The  type  and  blocks,  I  believe, 
last  longer  when  art  papers  are  used.  This  I  believe  to  be  due  to 
the  enamel  wearing  the  type  less  than  an  ordinary  sheet  of  paper 


31 


does.  An  art  paper  is  extremely  opaque,  due  to  the  large  amount 
of  mineral  matter  it  contains.  It  has  a  dead  or  chalky-white 
appearance.  It  may  be  said  to  bear  the  same  relationship  to  a 
sheet  of  pure  fibre  paper  that  earthenware  does  to  porcelain.  The 
very  translucency  of  pure  paper  gives  it  a  superior  and  I’efined 
appearance.  Immediately  you  render  a  paper  dead  opaque  to  light 
you  get  a  chalky  white.  In  its  behaviour  towards  reflecting  light 
there  is  this  important  difference  between  a  glazed  sheet  of  coated, 
and  a  glazed  sheet  of  uncoated  paper :  with  a  coated  paper  there 
is  only  one  plane  of  reflection  which  is  incident  with  the  surface 
of  the  paper.  If  a  ray  of  light  meets  the  surface  at  an  angle  it  is 
reflected  en  masse  at  the  same  angle,  so  that  the  angle  of  reflection 
is  equal  to  the  angle  of  incidence  as  with  a  mirror.  In  an  uncoated 
paper,  the  fibres  of  wdiich  it  is  composed  present  to  the  light 
innumerable  surfaces  disposed  at  every  conceivable  angle.  When 
a  ray  of  light  strikes  the  surface  of  such  paper,  instead  of  being 
reflected  at  the  same  angle  it  is  reflected  at  innumerable  angles 
and  in  all  directions,  giving  to  the  eye  the  general  impression  of 
whiteness  and  without  glare.  For  reasons  above  given  art  papers 
are  most  fatiguing  to  the  eye  when  used  for  printed  matter,  and 
it  is  not  to  be  wondered  at  that  so  many  of  the  public  have  raised 
their  voice  against  its  use  for  this  purpose. 

I  should  mention  that  the  paper  used  for  enamelling,  although 
its  composition  is  not  very  material,  should  possess  certain  pro¬ 
perties.  It  should  be  rosin  sized,  but  not  hard  sized.  It  should 
not  expand  much  when  wetted  by  the  enamel  solution  or  it  is 
liable  to  buckle.  If  too  hard  sized,  the  enamel  would  not 
penetrate  sufficiently  to  keep.  on.  The  surface  should  be  free 
from  dirt  and  grit  or  it  will  give  trouble. 

What  is  known  as  imitation  art  paper  is  generally  an  esparto 
paper  with  a  considerable  amount  of  mineral  in  it  and  perhaps 
some  wood  pulp,  and  slightly  rosin  sized,  treated  by  means  of  the 
water  doctor.  This  imparts  to  the  paper  what  is  known  as  the 
water  finish.  The  water  doctor  is  an  attachment  to  the  calenders 
which  holds  water  and  brings  the  surface  of  the  water  in  contact 
with  the  surface  of  the  paper  just  before  it  enters  the  nip.  Paper 
can  be  treated  in  this  way  either  on  one  or  both  sides.  The 
water  added  to  the  paper  in  this  way  has  to  be  extracted  by  the 
calenders.  A  double  stack  of  calenders  is  needed,  and  a  consider¬ 
able  amount  of  heat.  One  disadvantage  of  this  treatment  is  to 
very  materially  reduce  the  bulk  of  the  paper.  This  process  lays 
down  the  surface  of  the  paper  and  flattens  the  fibres  in  such  a 


32 


way  as  to  produce  a  somewhat  similar  effect  as  enamelling.  By 
squeezing  the  fibres  together  it  “brings  the  clay  to  the  surface” 
and  gives  the  appearance  of  coating  on  the  surface.  With 
enamelled  papers  the  colour  of  the  paper  itself  is  immaterial — 
the  colouring  matter  being  added  to  the  enamel.  Duplex  colours 
can  be  produced,  of  course,  by  means  of  enamelling.  The  water 
doctor  can  also  be  made  use  of  for  producing  duplex  colours  by 
placing  dyes  in  the  water. 

There  appears  to  be  some  confusion  with  regard  to  the  name 
“  Art "  paper.  I  take  it  that  the  name  originally  applied  to 
uncoated  papers  prepared  for  lithographic  work  and  art  illustration. 
Such  papers  were,  in  the  first  instance,  not  enamelled  at  all.  The 
name  has  got  to  be  applied  now  to  enamelled  papers,  and  the 
word  “  art  ”  is  now  written  in  inverted  commas.  What  is  now 
known  as  imitation  art  paper  is  paper  treated  with  the  water 
finish. 


References.— See  Parer  and  Pull*,  December  15th,  1901,  and  January  1st,  1902: 
“  Manufacture  of  Art  Papers,”  by  a  Reorder.  Read  also  Paper  and  Pulp,  May  15th,  1902: 
Photography  as  applied  to  Illustration  and  Printing:.  Lecture  I.,  Journal  of  Society  of 
Arts,  September  19th,  1902.  “The  Story  of  Photography,”  by  Alfred  T.  Story.  (George 
Newnes,  Ltd.)  See  also  various  articles  contributed  to  the  Paper  Trade  Review  in  1896 
by  R.  W.  Sindall  on  “Fillers,  and  their  Compositions.” 


LECTURE  III 


BLEACHING. 

Peculiarities  of  ultimate  fibres — Relative  lengths — Characteristics — Nature 
of  “  chloride  of  lime  ” — As  powder — In  solution — Table  of  strengths — 
Effects  of  heat  and  time  on  the  storage  of  bleaching  powder — Change  of 
strength  on  storage  of  solution — Chlorine  gas — Tumbler  bleaching— 
Bleaching  in  beater — Effects  of  carbonic  acid  gas  on  bleaching  solution — 
The  Thompson  process  —  Eau  de  Javelles  —  Relative  efficiencies  of 
different  solutions. 


Some  of  the  students  have  asked  me  to  describe  to  them  the 
general  characteristics  of  the  chief  papermaking  fibres.  These 
are  described  in  the  various  text-books  on  papermaking,  but 
often  in  a  way  which  is  not  intelligible  to  the  uninitiated  mind. 
In  my  lectures  before  the  Dickinson  Institute  I  endeavoured  to 
present  a  mental  picture  of  the  various  fibres  used  in  papermaking. 
I  cannot  do  better  than  give  you  extracts  from  these  lectures. 

What  is  needed  in  order  to  obtain  a  mental  grasp  of  any 
minute  object  is  a  model  of  this  object  on  a  large  scale,  such  as 
has  been  so  successfully  accomplished  at  the  South  Kensington 
Museum  in  the  case  of  the  malarial  mosquito  and  the  tsetse  fly. 
These  insects  have  been  reproduced  about  eight  inches  long,  every 
hair  and  every  detail  being  shown,  and  giving  an  impression  of 
being  alive. 

If  we  can  have  models  of  papermaking  fibres  on  a  magnified 
scale  produced  in  a  similar  way,  we  should  be  able  to  form  a  true 
mental  picture  of  their  various  characteristics,  far  better  than  we 
are  able  to  do  at  present  by  means  of  the  microscope. 

*  Cotton  fibre  is  a  tube  with  a  fairly  large  hole  or  canal 
through  the  centre,  but  through  the  walls  being  comparatively 
thin  this  tube  has  collapsed,  and  through  collapsing  it  has  assumed 
a  most  curious  shape,  and  it  is  principally  this  which  adds  to  its 
value  from  a  papermaker’s  point  of  view. 


*  Dickinson  Institute  Lecture,  October  25th,  1901. 


li 


34 


I  shall  endeavour  to  show  you  how  this  fibre  assumes  its 
corkscrew  appearance.  If  you  take  an  ordinary  piece  of  india- 
rubber  tube,  and  stop  up  one  end,  and  then  suck  the  air  out  of 
it,  you  cause  that  tube  to  collapse,  and  I  shall  endeavour  to  show 
you  the  effect  this  has  upon  a  piece  of  tube. 

Now,  this  tube  has  collapsed,  as  you  see  here,  and  if  it  is 
wound  round  like  this,  it  as  near  as  possible  resembles  the  cotton 
fibre  as  we  have  it  in  nature;  it  is  really  a  collapsed  tube.  The 
twist  is  occasioned  through  the  walls  being  irregular  in  thickness, 
as  this  tube  is.  This  causes  it  to  have  a  few  corkscrew  turns  in 
it,  even  when  I  do  not  give  it  a  turn  with  my  hand.  A  single 
cotton  fibre  has  anywhere  from  15  to  300  twists,  counting  from 
end  to  end. 

Now,  if  it  were  not  for  its  peculiar  corkscrew  twists  when 
the  fibres  interlace  one  with  another,  cotton  would  not  bulk  paper 
as  it  does.  Take  a  number  of  chair-springs  and  pack  them  as 
close  as  you  can,  you  cannot  prevail  upon  the  wires  to  go  close 
together,  but  if  you  pull  the  wires  out  and  make  them  straight 
they  will  pack  close.  iVe  may  regard  the  straight  wires  as  linen, 
and  the  springs  as  cotton,  and  we  have  some  rough  idea  of  the 
paper  from  each. 

The  cotton  fibre  is  immensely  strong,  and  a  single  tiny  fibre 
is  capable  of  supporting  an  enormous  weight  in  comparison  with 
its  thickness.  You  must  try  and  realise  that  the  interlacing  of 
the  fibres  is  like  clasping  the  two  hands  together ;  if  we  clasp 
hands  and  pull,  we  give  way  because  our  muscular  strength  fails  ; 
we  can’t  hang  on  until  the  bones  break. 

*■  Straw  and  esparto  occupy  an  entirely  different  position 
to  cotton  and  linen.  The  effect  produced  by  any  fibre  for  the 
purpose  of  paper  manufacture  can  always  be  traced  to  the  form, 
size,  and  chemical  behaviour  of  the  ultimate  fibre  itself.  There 
is  a  reason  why  a  particular  fibre  gives  a  particular  result,  and 
you  can  trace  the  result  right  back  to  the  form  of  the  fibre  as 
seen  under  the  microscope. 

Straw  is  the  shortest  of  the  papermaking  fibres  ;  you  would 
have  to  put  75  fibres  one  on  the  end  of  the  other  to  equal  the 
length  of  one  cotton  fibre ;  it  is  a  stumpy  fibre  as  compared 
with  cotton,  as  it  is  thick  in  comparison  with  its  length.  Esparto 
is  much  longer  than  straw,  although  much  shorter  than  cotton : 
some  straw  fibres  are  quite  as  thick,  whilst  others  have  about 
half  the  thickness  of  the  cotton  fibre. 


Dickinson  Institute  Lecture,  November  1st,  1901. 


35 


I  have  a  table  here  which  I  thought  perhaps  would  give  you 
some  idea  of  the  relative  lengths  of  fibres.  We  take  cotton  and 
linen  fibres  as  equal  to  one  inch  in  length.  The  table  further 
demonstrates  that  m  ordinary  beating  the  cotton  fibre  is  divided 
into  about  30  pieces.  The  first  column  of  the  table  shows  the 
number  of  fibres  to  the  inch,  the  second  column  shows  the 
number  of  fibres  necessary  if  placed  side  by  side  to  equal  an  inch 
m  thickness. 

m*igiy.e,this  in  °rder  that  you  may  be  able  to  form  some 
mental  picture  of  the  difference  in  size,  &c.,  in  the  fibres  as  they 
ex!st  in  the  paper  You  will  realise  more  readily  afterwards 
of  paper6  ^  W  their  peculiar  effect  upon  the  properties 


No.  of  fibres 
per  inch 
lengthwise. 

Fibres  per 
inch  placed 
side  by 
side.' 

Beaten 

Stuff 

No.  per 
inch. 

Fibres  cut 
during-  beat- 
ing'into 
about 

Cotton.  . 
Linen  . . 
Straw  .  . 
Esparto 

1 

1 

75 

18 

1,200 

1,200 

1,250 

2.200 

30 

30 

75 

25 

30  pieces 
30  „ 

Not  cut 
About  1 

Straw  is  so  short  that  it  is  not  cut  by  the  beater  knives. 
Jcisparto  being  somewhat  longer  is  occasionally  cut,  but  two  out 
ot  every  three  fibres  escape  the  cutting  of  the  knives  altogether. 

In  the  case  of  wood  it  is  a  different  matter.  The  wood  fibres 
vary  so  much  m  character,  some  are  long  and  some  are  short  •  so 
you  cannot  give  an  average  of  the  length  of  fibre,  or  estimate 
the  number  of  pieces  into  which  the  fibres  are  cut  by  the  action 
ot  the  beater  roll. 

^,0'v’  h1,  regard  to  straw,  there  are  certain  characteristic 
vessels  by  which  you  can  distinguish  it  from  any  other  paper¬ 
making  material;  they  are  known  as  the  Parenchyma  vessels,  and  are 
peculiar  oval  cells,  one  on  the  end  of  the  other.  There  are  also 
a  number  of  curious  serrated  cells,  which  are  common  to  both 
esparto  and  straw,  and  I  think  you  will  remember  the  appearance 
of  these  cells  best  if  I  tell  you  they  are  like  the  edge  of  a  piece  of 
corrugated  iron.  The  esparto  fibre  is  always  recognised  by  its 
fine  hairs,  resembling  sharp  teeth.  If  you  stroke  down  a  small 
piece  ot  esparto,  as  you  pass  your  fingers  along  you  can  feel  a 


b  2 


36 


number  of  small  hairs,  very  fine  indeed,  millions  of  them ;  these 
help  you  to  distinguish  esparto  from  any  other  fibres. 

That  esparto  fibre  which  is  really  the  papermaking  fibre  has 
very  thick  walls  and  only  a  small  hole  through  the  centre :  the 
ends  are  solid  and  rounded,  whilst,  unlike  the  cotton  fibre,  the  hole 
through  the  centre  is  so  small  that  it  will  not  allow  the  tube  to 
collapse.  There  is  something  very  curious  that  happens  with 
these  fibres  when  they  grow  side  by  side ;  they  are  pressing  one 
another  very  hard,  and  instead  of  being  round  they  often  get 
into  a  peculiar  shape — six-sided,  like  honeycomb.  With  many 
fibres  this  is  the  case ;  it  is  due  to  the  fibres  whilst  growing 
pressing  one  upon  the  other,  and  producing  a  six-sided  figure. 

The  straw  fibre  is  smoother  on  its  surface,  and  more  polished 
than  esparto,  and  is  very  much  more  inclined  to  take  up  water ; 
it  works  wet,  and  in  this  respect  is  somewhat  different  to  esparto 
in  its  papermaking  qualities,  which  will  be  explained  presently ; 
this  is  one  of  the  great  distinguishing  features  between  esparto 
and  straw. 

When  the  wood  has  been  chemically  treated  the  fibres  to  a 
large  extent  lose  their  characteristics.  Sometimes  the  wood  fibre 
has  a  number  of  lattice-work  markings  on  the  surface,  as  in  the 
case  of  spruce.  Spruce  is  a  wood  which  is  used  in  America,  in 
place  of  pine,  much  more  extensively  than  in  this  country.  It  is 
not  at  all  surprising  that  different  kinds  of  wood  yield  different 
qualities  of  pulp,  and  produce  such  a  divergence  in  the  qualities 
of  paper ;  it  is  only  necessary  to  glance  at  the  various  published 
diagrams  to  appreciate  this  fact.  By  the  judicious  choice  of 
wood,  and  also  by  modifying  both  the  mechanical  and  chemical 
treatment  it  can  be  made  to  produce  papers,  on  the  one  hand 
resembling  a  strong  linen  bank,  to  soft  papers  on  the  other  hand 
which  are  made  to  do  service  in  place  of  esparto.  I  am  told  that 
it  can  be  made  to  produce  good  filter  paper. 

*  Many  wood  fibres  resemble  cotton,  in  that  they  are 
collapsed  or  flattened  cells,  but  the  cell  walls  being  thinner  in 
comparison  with  the  diameter,  the  fibre  does  not  present  that 
curious  appearance  noticeable  in  cotton.  Being  consequently 
more  flattened,  like  an  elongated  envelope,  when  seen  in  section, 
it  does  not  present  the  appearance  of  having  the  edges  turned  up 
to  the  extent  that  cotton  has.  Occasionally  the  wood  fibre  is 
found  to  be  folded  on  itself,  but  from  its  more  flattened  nature  it 


Dickinson  Institute  Lecture,  November  15th,  1901. 


37 


never  presents  that  peculiar  corkscrew  appearance  so  character¬ 
istic  of  cotton. 


The  pine  wood  has  on  its  surface  pitted  vessels  or  pores, 
generally  presenting  the  appearance  of  one  circle  within  the 
other.  No  two  kinds  of  timber  present  the  same  appearance 
under  the  microscope,  and  even  the  time  of  year  at  which  the 
timber  has  been  felled  affects  the  general  appearance  as  well  as 
the  dimensions  of  the  isolated  fibre.  I  should  like  to  point  this 
out,  as  it  is  not  generally  known.  Taking  pinewood,  for  instance, 
the  fibres  that  are  only  one  year  old  are  shorter  than  others  that 
have  reached  their  full  growth ;  when  a  tree  has  reached  its  full 
development  the  fibres  are  much  longer. 

If  you  take  fibres  that  are  only  one  year  old,  you  would 
require  25  fibres  lengthwise  to  make  an  inch;  seventeen  years 
old  ten  fibres  per  inch,  and  fifty  years  old  eight  per  inch ;  at  fifty 
years  old  they  have  reached  their  full  length.  Pine  wood  yields 
long  soft  fibres.  Mechanical  wood  produced  from  pine,  when 
magnified,  gives  perhaps  the  best  idea  of  the  general  character¬ 
istics  of  wood ;  the  fibres  are  ranged  side  by  side  as  in  the  form 
of  a  raft,  and  generally  shows  medullary  rays  in  the  form  of  cross 
markings,  and  the  pitted  vessels  are  most  prominent. 

With  these  preliminary  remarks  on  the  subject  of  paper¬ 
making  fibres,  we  will  proceed  to  the  subject  of  this  evening’s 
lecture.  & 

Before  attempting  to  go  into  the  subject  of  bleaching  from 
a  papermaker  s  standpoint,  we  must  give  some  idea  of  the 
preparation  and  chemical  nature  of  ^chloride  of  lime  or  bleaching 
powder. 


This  well-known  body  was  originally  considered  to  be  a 
compound  of  chlorine  and  lime.  Balard,  in  1834,  was  the  first 
to  give  an  explanation  of  the  constitution  of  this  compound,  and 
his  explanation  has  from  that  time  been  generally  adopted. 
According  to  this  view,  bleaching  powder  is  a  mixture  of  calcium 
hypochlorite  and  calcium  chloride  Ca(OCl),  +  CaCL.  Another 
\iew  of  the  constitution  of  bleaching  powder  has  been  taken  by 
Odling.  He  looks  upon  this  substance  as  a  kind  of  double  salt, 

( OC1,  beino  ^be  ^me  time  a  chloride  and  a  hypochlorite. 

Chloride  of  lime  is  obtained  by  the  action  of  chlorine  gas 
upon  dry  slaked  lime.  When  chlorine  is  passed  into  milk  of 


*  Roscoe  and  Schorlemmer,  Part  1,  Vol.  2,  pages  194  and  197. 


38 


lime,  a  reaction  which  is  analogous  to  the  formation  of  Eau  de 
Javelle  (Yol.  1,  page  264)  takes  place. 


2  Ca(OH,)  +  2  Cl,=CaCL+Ca(0CU+2H.,0. 


If,  however,  dry  slaked  lime  be  employed,  a  large  proportion  of 
the  lime  remains  unaltered.  This  fact  was  formerly  explained  by 
the  supposition  that  the  calcium  chloride  produced  forms  a 
coating  round  the  particles  of  lime,  which  prevents  the  further 
action  of  the  chlorine.  But  even  if  the  mixture  be  from  time  to 
time  well  rubbed  down  in  a  mortar,  and  then  again  treated  with 
chlorine,  it  is  not  possible  to  obtain  a  material  containing  more 
than  40  per  cent,  of  available  chlorine.  Hence  this  substance 
would  appear  to  be  a  mixture  of  basic  salt  with  chloride  of 
calcium,  according  to  the  formula. 


3Ca(OH),+2CL=2Ca  j  +CaCl2+2H20. 


If  water  be  added  to  this  product  the  soluble  chloride  dissolves, 
and  the  basic  hypochlorite  decomposes  as  follows : — 


In  practice  it  is  found  that  11  cwt.  of  caustic  lime  is  required 


to  form  one  ton  of  bleaching  powder.  In  the  preliminary  slaking 
and  dressing  of  the  lime  probably  1-^  cwt.  is  lost.  The  lime  ready 
for  use  contains  about  25  per  cent,  of  water,  and  1.2  per  cent,  of 
carbon  dioxide,  so  that  20  cwt.  of  bleaching  powder  would  be 
made  up  as  follows  :  — 

Lime..  ..  ..  ..  ..  ..  ..  9.5  cwt. 

Water,  25  per  cent,  on  the  100  of  hydrated  lime  3.2  ,, 

Chlorine,  35  per  cent,  on  the  finished  B.P.  .  .  say  7.3  „ 


20.0  cwt.  B.P. 


*Bleaching  powder  is  made  into  solution  by  prolonged 
agitation  or  stirring  with  water.  Cast  iron  is  a  suitable  metal 
for  containing  the  liquid,  steel  and  wrought  iron  are  acted  upon. 
After  the  sediment  has  been  allowed  to  settle,  the  clear  liquid  is 
drawn  off,  and  the  sediment  or  grouts  further  exhausted  by 
agitation  with  water.  The  bleach  grouts  are  thrown  away. 

It  is  useful  for  us  to  have  some  ready  means  of  gauging  and 
estimating  the  strength  of  our  bleach  solutions. 

Some  time  ago  I  constructed  a  table  for  the  use  of  paper- 
makers  from  the  observations  made  by  Lunge  and  Bachofen,  to 


*  See  “  The  Specific  Gravity  of  Bleach  Solutions”  (Beadle),  Chemical  Trade  Journal, 
No.  323. 


39 


enable  those  in  the  mill  to  determine  at  a  glance  the  strength  of 
a  bleaching  powder  solution,  expressed  in  pounds  of  dry  bleaching 
powder  per  10  gallons,  after  merely  gauging  it  with  a  Twaddle 
hydrometer. 


Degrees 

Twaddle. 

Pounds  of 
bleaching 
powder  per 

10  gallons. 

Degrees 

Twaddle. 

Pounds  of 
bleaching 
powder  per 

10  gallons. 

.0 

Trace 

12.0 

10.23 

.5 

.40 

13.0 

11.06 

1.0 

.77 

14.0 

12.09 

2.0 

1.59 

15.0 

13.06 

3.0 

2.42 

16.0 

13.99 

4.0 

3.26 

17.0 

14.93 

5.0 

4.14 

18.0 

15.77 

6.0 

4.96 

19.0 

16.66 

7.0 

5.84 

20.0 

17.48 

8.0 

6.79 

21.0 

18.43 

9.0 

7.61 

22.0 

19.43 

10.0 

8.40 

23.0 

20.43 

11.0 

9.34 

— 

— 

Apparently  the  only  basis  that  papermakers  had  to  go  on 
was  the  general  understanding  that  a  12°  Twaddle  solution 
contained  1  lb.  of  bleaching  powder  per  gallon. 

In  order  to  determine  the  strength  of  a  solution  with 
the  utmost  ease  and  rapidity,  it  is  best  to  take  10  c.c.  and  make 

up  to  100  c.c.,  and  titrate  10  c.c.  of  this  with  jq  arsenious  acid. 

The  number  of  c.c.  used  gives  lbs.  of  bleaching  powder  per  10 
gallons  without  calculation. 

Chemists  have  thoroughly  studied  the  keeping  properties  of 
the  bleaching  powder  as  sent  out  by  the  manufacturers.  In 
cold  weather  the  powder  may  contain  38  per  cent,  available 
chlorine,  in  very  hot  weather  it  may  be  difficult  to  produce  it  to 
contain  more  than  35  per  cent.  The  powder  deteriorates  only 
slowly  if  stored  in  a  cool  dry  place.  Heat  will  cause  it  to  lose 
its  chlorine  strength,  and,  if  damp,  it  will  deteriorate  either  in 
the  hot  or  cold. 

As  little  is  known  about  the  keeping  qualities  of  bleaching 
powder  solutions,  I  give  you  the  results  of  my  own  work:  — 

The  solution  taken  contained  1.85  per  cent,  available 
chlorine,  which  equals  5.55  per  cent,  bleaching  powder.  It 


40 


stood  at  7°  Twaddle.  On  the  first,  second,  and  third  days 
the  solution  was  found  on  titration  to  contain  1.85  per  cent, 
chlorine.  On  the  forty-third  day  it  contained  2.50  per  cent,  of 
chlorine,  and  on  the  seventy-second  day  the  solution  contained 
0.202  per  cent,  chlorine.  During  the  43  days  the  solution  had 
increased  35.1  per  cent,  in  chlorine  strength  it  originally 
contained,  and  during  the  72  days  the  solution  had  decreased  by 
89.2  per  cent,  of  the  chlorine  it  originally  contained.  This 
apparent  anomaly  is  due  to  the  fact  that  to  begin  with,  the 
evaporation  of  moisture  from  the  surface  was  far  more  rapid  than 
the  loss  of  chlorine. 

As  to  the  evaporation.  During  40  days  a  similar  solution 
to  that  taken  had  lost  weight  equal  to  15.88  per  cent.,  or  at  the 
rate  of  .397  per  cent,  per  diem.  During  53  days  the  solution 
had  lost  weight  equal  to  29.00  per  cent.,  or  at  the  rate  of  .547 
per  cent,  per  diem.  For  about  50  days  the  solution  underwent 
very  little  change  in  colour,  and  it  appears  that  up  to  a  certain 
stage  the  loss  by  weight  is  almost  entirely  due  to  the  evaporation 
of  water,  which  considerably  increases  the  percentage  strength  of 
available  chlorine.  That  little  or  no  chlorine  is  given  off  is 
evident  from  the  fact  that  the  loss  by  weight  in  43  days  is 
hardly  sufficient  to  account  for  the  increase  in  the  available 
chlorine  found  in  the  solution.  After  a  certain  period,  which 
appears  to  depend  somewhat  upon  the  temperature,  the  solution 
undergoes  a  more  rapid  change  in  colour,  becoming  much  paler, 
with  a  corresponding  diminution  in  chlorine  percentage.  The 
more  rapid  evaporation  during  the  later  periods  is  probably  due 
to  the  evolution  of  chlorine  or  hypochlorous  acid,  but  more 
probably  the  former.  There  appears  to  be  no  harm  in  storing 
bleach  in  tanks  for  six  weeks,  except  in  hot  weather,  the  loss  of 
chlorine  being  almost  inappreciable.  Beyond  this  time  a  rapid 
deterioration  sets  in.  There  is  every  reason  to  believe  that  there 
is  considerable  danger  in  half  emptying  a  store  tank  or  drawing 
from  a  tank,  the  large  bulk  of  which  is  allowed  to  remain  at  the 
bottom  for  the  most  part  undisturbed.  The  undisturbed  portion, 
if  allowed  to  remain  too  long,  may  deteriorate  and  induce  rapid 
deterioration  of  fresh  quantities  run  into  the  tank. 

Papermakers  and  other  large  consumers  of  bleach  who  have 
the  bleaching  liquor  pumped  up  to  a  head  and  distributed  by 
gravitation  through  mains  to  the  various  parts  of  their  works, 
should  look  into  this  matter  very  carefully. 

The  above  experiments  of  course  apply  only  to  the  actual 
conditions  under  which  these  trials  were  conducted.  It  stands  to 


41 


SSSsH^r-- 

==X,S.“,,s»S2:b“.= 

about  its  chemical  properties  °et  us'see0"  h'f  k“°W  sometllillg 
the  way  of  its  ecLomLal  ’uttlisati™  •  ^  1;?"  SUgges>  “ 
not  taoubfeabout  -jjp-  and .descriptions  as  gi™  iS 

wa^ obtained  by  Ictog  7„n  “““““g  agentP°  itis 

%i:iSBSSiSl=Ss 

•  s0fer“Sf  TberS°me  °pel'ation’  “<*  aHbough1  effective 
to  apply  to  wooadhlp®r  “0“'  X™  ^  ^ 

represented,  is  vert  L?  V  i,  “  Tl  as  g“e™% 
according  to  the  following  equation  PP°Setl  to  tate  Place 
Cl,  +  H,0  =  2HC1  +  o 
Chlorine  Water  Hydrochloric  Bleaching 

calciuafh^blSnt:(PcI(Ootring  ^  “  S“tetouce  called 

Bleaching  powder  can  be  readily  dissolved  in  water  to  n  in 

“Possible  EoLdorafe?etoabegEfflctednfnhn?  th.e.  fol,!°7in?  article,  now  out  of  print  — 
World’s  Number,  1§96  ted  m  BleaoIllng  (Beadle),  Paper. Maker, : ‘special 


42 


receptacle,  of  the  shape  of  a'  sulphite  digester,  known  as  a 
tumbler,  lined  with  lead,  is  filled  with  rags,  and  a  quantity  of 
dilute  bleach  solution  added.  To  this  is  added  a  small  quantity 
of  vitriol.  The  man-hole  door  is  fastened  on  and  the  tumbler 
made  to  revolve.  This  is  kept  in  motion  for  about  24  hours,  • 
and  then  the  liquor  is  drained  off  into  a  tank,  and  is  used  again 
in  a  new  batch.  This  method  of  bleaching  consumes  a  large 
quantity  of  bleaching  agent  besides  taking  a  long  time.  It  is 
necessary  that  the  rags  should  not  be  stored  for  any  length  of 
time  before  being  placed  in  the  breaker  for  washing,  as  they  are 
liable  to  become  tendered  by  the  presence  of  the  acid.  Instead  of 
bleaching  the  x’ags,  the  half-stuff  is  often  bleached  in  the  poacher 
or  in  a  chest  into  which  the  poacher  discharges.  This  takes 
from  10  to  20  hours,  and  is  often  accelerated  by  the  addition 
of  a  small  quantity  of  acid.  The  third  method  of  bleaching  rag 
fibre  is  to  add  the  bleach  to  the  beater,  and  to  allow  the  bleaching 
to  take  place  during  the  beating  of  the  fibre. 

I  have  carefully  compared  these  three  methods  of  bleaching, 
and  have  come  to  the  conclusion  that,  as  regards  the  amount  of 
chlorine  actually  consumed,  the  third  method  is  by  far  the  most 
economical ;  hut  when  we  come  to  take  into  consideration  the 
fact  that,  in  order  to  get  the  bleaching  done  in  the  time  it  is 
necessary  to  add  about  twice  the  amount  of  bleaching  powder 
actually  consumed,  and  as  it  is  often  impossible  to  use  a  washing 
drum  on  the  bleached  stuff  the  unconsumed  half  of  the  bleaching 
powder  has  to  be  neutralised  by  the  addition  of  an  antichlor,  we 
find  the  method  is  expensive.  The  following  are  two  sets  of 
tests. 

1  give  you  here  the  conditions  of  some  of  the  trials  in  the 
beater.  My  conclusions  are  not  based  upon  one  or  two  solitary 
trials,  but  upon  a  large  number  of  a  similar  nature : — 

(1.)  Third  quality  linens  in  beater. — 224  lbs.  dry  material, 
5.14  lbs.  bleaching  powder,  added  in  the  form  of  a  solution. 
This  equals  .802  per  cent,  of  chlorine  on  dry  fibre.  Residual 
liquor  after  three  hours’  action  contained  .0192  per  cent, 
chlorine.  As  the  beater  contained  4,560  lbs.  of  solution,  it 
contained  at  finish  .875  lb.  of  chlorine,  or  about  2\  lbs.  of 
bleaching  powder  unconsumed.  Therefore,  the  amount  actually 
used  up  in  the  bleaching  was  just  about  half  the  amount 
originally  added. 

(2.)  Third  quality  cotton  rags  in  beater. — 224  lbs.  dry  fibre, 
bleach  liquor  added  equal  to  7.2  lbs.  of  bleaching  powder,  which 
equals  2.52  lbs.  of  chlorine.  This  equals  1.12  per  cent,  of 


43 


chlorine  on  the  weight  of  dry  fibre.  The  residual  liquor  after 
three  hours’  action  was  found  to  contain  .020  per  cent,  of 
chlorine,  which  is  equal  to  a  total  weight  of  .912  lb.  of  residual 
chlorine  in  the  engine,  which  equals  .407  per  cent,  on  dry  fibre. 
In  this  case,  65  per  cent,  of  the  total  amount  of  bleaching 
powder  added  was  used  up  in  the  bleaching. 

If  it  is  found  necessary  to  hurry  the  bleaching  more,  we 
must  add  larger  quantities  of  bleach  liquor,  and  the  result  is 
that  a  larger  proportion  of  bleach  is  left  unconsumed.  By 
comparing  these  and  similar  results  in  the  engine  with  tumbler 
bleaching,  I  concluded  that,  for  the  actual  amount  of  chlorine 
consumed,  bleaching  in  the  beater  was  much  more  economical, 
but  on  account  of  the  necessity  of  adding  a  chemical  to  neutralise 
the  free  chlorine  remaining  the  total  cost  was  greater.  The 
reasons  that  the  actual  amount  of  chlorine  consumed  in  the 
beater  is  so  much  less  appear  to  me  to  be  as  follows : — Firstly, 
the  rags  are  to  a  large  extent  cleansed  of  dirt  when  washed  in 
the  breaker.  This  dirt  would  consume  some  of  the  bleach. 
Secondly,  the  rapid  agitation  of  the  beater-roll  accelerates  the 
action  of  the  bleach.  It  is  always  found  more  economical  to 
agitate  during  the  bleaching.  Thirdly,  apart  from  the  actual 
agitation,  the  beater-roll  aerates  the  stuff  and  brings  it  also  in 
contact  with  the  carbonic  acid  of  the  atmosphere.  The  carbonic 
acid  helps  to  set  free  hypochlorous  acid,  which  is  more  active 
and  economical  in  its  action  than  when  combined,  as  calcium 
hypochlorite.  The  change  takes  place  according  to  the  following- 
equation. 

Ca  (CIO)*  +  C02  =  CaC03  +  2HCIO 

Bleaching  Carbon  Chalk  Hypochlorous 

Powder  Dioxide  Acid 

As,  however,  the  atmosphere  only  contains  about  four  parts  of 
carbonic  gas  per  10,000,  the  action  is  comparatively  slow'.  The 
application  of  carbonic  acid  in  connection  with  bleaching  powder 
solution  was  patented  in  1855  by  P.  F.  Didot,  and  in  1883 
Thomson  patented  a  process  in  which  he  used  carbonic  acid  to 
accelerate  the  action  of  the  bleaching  powder  solution  for  the 
bleaching  of  fabrics.  This,  however,  was  never  used  successfully, 
as  far  as  I  am  aware,  for  the  bleaching  of  rag  stuff.  It  consisted 
in  exposing  the  cloth  under  treatment  alternately  to  the  action 
of  the  bleaching  powder  solution  and  carbonic  acid  gas.  I  have 
seen  Thomson’s  process  applied  to  rags  in  a  closed  chamber  by 
damping  rags  with  weak  bleach,  placing  same  into  chamber,  and 
passing  in  C02.  If  the  C02  had  been  introduced  as  a  slow  stream 


44 


in  front  of  beater-roll,  the  process,  in  my  opinion,  would  have 
stood  a  good  chance  of  success.  In  practice  the  difficulty  which 
presents  itself  is  the  production  of  C02.  This  might  be 
accomplished  either  by  using  a  carboniser  such  as  is  used  in 
Archbutt  and  Deeley’s  water-softening  plant,  or  when  practicable 
the  furnace  gases  might  be  employed.  Both  gases  might  need 
to  be  washed  through  water  to  remove  any  sulphurous  acid, 
which  if  allowed  to  remain  would  act  as  an  antichlor. 

In  order  to  accelerate  the  action  of  bleaching  powder 
solution,  I  have  passed  carbonic  acid  through  a  2  per  cent, 
solution  until  the  lime  was  thrown  down.  I  have  found  this  far 
more  rapid  in  bleaching  effect  than  ordinary  bleach  solution. 
A  single  experiment  will  demonstrate  this. 

Ordinary  bleaching  powder  solution  of  the  above  strength 
turns  a  red  litmus  paper  blue  on  account  of  the  free  lime  that  it 
contains,  at  the  same  time  it  only  slowly  bleaches  the  litmus. 
On  passing  through  carbonic  acid  the  solution  becomes  milky 
through  the  formation  of  carbonate  of  lime.  This  turns  blue 
litmus  paper  red  on  account  of  the  presence  of  free  hypochlorous 
acid  in  solution  ;  in  addition  to  this  the  paper  is  rapidly 
bleached.  The  equation  is  as  follows 

Ca(C10)2  +  C02  =  CaC03  +  2HC10. 

If,  however,  the  carbonic  acid  is  added  in  sufficient  quantities 
to  re-dissolve  the  lime,  we  have  a  solution  containing  bicarbonate 
of  lime  and  hypochlorous  acid  together.  This  gives  an  acid 
reaction  with  iitmus,  and  for  some  purposes  is  a  safer  solution 
to  use  for  bleaching  than  the  one  previously  described,  and  for 
the  following  reason.  The  milky  precipitate  formed,  when  only 
sufficient  carbonic  acid  is  added  to  precipitate  all  the  lime,  if 
allowed  to  settle,  as  is  the  case  when  the  liquid  is  stored  in  a 
tank,  leaves  a  solution  containing  nothing  but  hypochlorous  acid. 
When  this  is  used  for  bleaching,  free  hydrochloric  acid  is  formed, 
which  by  some  process  or  other  must  be  neutralised — 

HCIO  =  HC1  +  O 
Hypochlorous  Hydrochloric  Bleaching 

Acid  Acid  Oxygen 

When  sufficient  carbonic  acid  is  used  to  redissolve  the  chalk 
precipitate,  we  obtain  bicarbonate  of  lime  in  solution,  which  will 
prevent  the  formation  of  hydrochloric  acid  by  the  formation 
of  calcium  chloride — 

CaC03C02  +  2HC10=  CaCl2  +  1I20  +  2C02+  O 
This  solution  has  the  advantages  of  ordinary  bleaching  powder, 
without  its  disadvantages.  It  is  extremely  active  and  economical, 


45 


whereas  bleaching  powder  is  sluggish  and  wasteful  in  its  action. 
Furthermore,  it  has  the  advantage  over  free  hypochlorous  acid,  in 
that  there  is  no  formation  of  free  hydrochloric  acid  after 
bleaching. 

I  do  not  think  that  it  is  generally  known  that  so  much 
depends  upon  how  the  hypochlorites  are  made  and  used.  There 
is  room  for  immense  improvements  and  very  substantial 
economies,  if  the  knowledge  which  we  now  possess  is  followed 
up  and  taken  advantage  of. 

Until  the  discovery  of  Hermite’s  solution,  it  was  generally 
supposed  that  1  lb.  of  chlorine  would  do  a  definite  amount  of 
bleaching.  This,  however,  was  disproved  when  Hermite’s  solution 
was  compared  with  bleaching  powder.  Hermite’s  bleaching 
solution  is  produced  by  electrolising  a  dilute  solution  of 
magnesium  chloride,  and  in  his  later  patent  by  electrolising  a 
mixture  of  common  salt  and  magnesium  chloride.  The  bleaching 
substance  formed  is  magnesium  hypochlorite,  Mg(C10)2.  On 
taking  two  solutions,  one  of  bleaching  powder  and  the  other 
produced  by  Hermite’s  process,  containing  equal  amounts  of 
chlorine,  the  latter  was  found  to  bleach  wood  pulp  much  more 
rapidly  than  the  former,  and  when  the  action  was  complete,  for 
every  5  lbs.  of  chlorine  consumed  in  the  former  solution,  only 
3  lbs.  were  consumed  in  the  latter.  These  claims  were  fully  set 
forth  by  the  inventor,  and  have  been  verified  by  Messrs.  Cross  & 
Bevan,  Professor  Pictet,  and  myself.  Cross  &  Bevan  and 
Pictet  made  their  determinations  upon  wood.  I  made  a  series 
of  experiments  in  the  beater  with  different  qualities  of  rags. 
In  each  case  I  found  the  relative  efficiencies  to  be,  as  near  as 
possible,  as  above  stated — namely,  as  3  is  to  5.  It  is  not  yet 
known  why  the  chlorine  in  the  two  solutions  acts  differently, 
but  I  shall  endeavour  to  give  an  explanation  or  a  theory  that  may 
possibly  account  for  it  in  my  next  lecture. 

Before  the  discovery  of  bleaching  powder  by  Tennant  in 
1798,  Bertholiet  found  that  chlorine  could  be  absorbed  by  a 
solution  of  caustic  potash,  and  the  solution  possessed  the  same 
bleaching  properties  as  the  gas.  This  solution  is  known  to  this 
day  as  Eau  de  Javelles.  It  was  extensively  used  on  the 
Continent  for  bleaching  purposes.  The  active  principle  of  this 
solution  is  potassium  hypochlorite.  It  is,  however,  too  expensive 
to  compete  with  bleaching  powder.  A  solution  somewhat 
similar  in  properties  to  this  can  be  prepared  by  adding  sodium 
carbonate  solution  to  a  solution  of  bleaching  powder.  The 


46 


active  principle  in  this  is  sodium  hypochlorite.  It  is  formed 
according  to  the  following  equation  :  — 

0a(C10)2  +  Na,CO,  =  CaC03  +  2NaC10. 

Bleaching  powder  and  carbonate  of  soda  gives  chalk  and 
sodium  hypochlorite.  The  chalk  formed  is  allowed  to  settle  out. 
This  solution  is  used  in  some  mills  in  place  of  bleaching 
powder  solution.  It  offers  certain  advantages  which  will  be 
pointed  out  hereafter.  Some  works,  instead  of  buying  bleaching 
powder  and  converting  it  into  a  solution,  generate  chlorine  gas, 
which  is  bubbled  through  a  solution  of  milk  of  lime. 

By  this  last-mentioned  process  calcium  hypochlorite  is 
formed.  But  this  solution,  although  generally  considered 
chemically  identical  with  that  obtained  from  bleaching  powder, 
is  very  different  in  bleaching  effect.  It  is  generally  known 
that  these  solutions  behave  differently  from  each  other  as 
regards  their  rate  of  bleaching,  and  it  is  supposed  that  hypo¬ 
chlorite  is  much  more  sluggish  in  its  action  than  bleaching 
powder  solution. 

In  order  to  see  which  form  of  bleaching  liquor  was  most 
economical  I  prepared  three  solutions  as  follows : — 

(a)  A  solution  prepared  by  passing  chlorine  gas 
through  milk  of  lime. 

(b)  A  solution  of  ordinary  bleaching  powder. 

(<j)  A  solution  of  sodium  hypochlorite,  prepared  by 
adding  carbonate  of  soda  to  bleaching  powder  solution, 
as  previously  described. 

The  available  chlorine  of  each  of  these  solutions  was 
carefully  determined,  and  water  was  added  to  each  in  sufficient 
quantity  to  make  the  strength  equal  to  exactly  5  grammes  oi 
chlorine  per  litre.  I  took  5  grammes  of  unbleached  wood  pulp 
and  mixed  it  with  200  c.c.  of  water,  and  after  thoroughly 
pumping  I  added  200  c.c.  of  solution  a.  By  the  side  of  this  I 
treated  solutions  b  and  c  in  a  similar  manner. 

After  1 9  hours’  action  the  wood,  in  each  case,  was  bleached. 
I  withdrew  equal  quantities  of  solution  from  each,  and  determined 
the  amount  of  chlorine.  As  each  solution  was  diluted  with  its 
own  volume  of  water,  the  solution  in  contact  with  the  pulp  was 
equal  at  the  start  to  2|  grammes  per  litre  of  chlorine. 


47 


After  the  bleaching  the  chlorine  determinations  were  as 
follows : — 

In  Solution.  Consumed. 

(a)  1.777  per  cent.  .725  per  cent. 

(b)  1.296  „  1.204 

(c)  1.(57  ,,  .743  ,, 

It  will  be  seen  from  the  above  that  bleaching  powder  solution 
is  the  least  economical  of  the  three.  Supposing  that  with 
bleaching  powder,  in  order  to  bleach  a  certain  weight  of  wood, 
pulp  we  consume  100  lbs.  weight  of  chlorine  for  a  milk  of  lime 
solution.  Satui'ated  with  chlorine  gas  we  should  require  only 
60  lbs.  weight  of  chlorine,  added  in  the  form  of  a  solution 
of  sodium  hypochlorite.  It  will  be  seen,  therefore,  that,  it  is 
not  fair  to  base  the  value  of  a  bleaching  solution  merely  on 
the  amount  of  available  chlorine  that  it  contains.  It  is  necessary, 
in  addition  to  this,  to  determine  what  amount  of  bleaching  work 
the  chlorine  is  capable  of  doing.  It  appears  that  the  bleaching 
effect  of  chlorine  depends  largely  upon  the  state  of  its 
combination.  AVhy  this  is  so  nobody,  so  far,  has  been  able  to 
discover.  It  has  generally  been  supposed  that,  as  previously 
explained,  the  chlorine  acts  upon  water,  decomposing  it,  forming 
hydrochloric  acid  and  liberating  oxygen,  and  that  the  oxygen  is 
really  the  bleaching  agent.  Ordinary  oxygen,  such  as  the 
greater  part  of  the  oxygen  contained  in  the  atmosphere,  is 
incapable  of  bleaching,  but  ozone,  which  is  obtained  by 
electrifying  ordinary  oxygen,  is  a  powerful  bleaching  agent. 

If  the  above  theory  of  bleaching  is  correct,  it  may  be  that 
the  oxygen  formed  during  the  bleaching  is  only  in  part  active. 
The  efficiency  then  of  a  bleaching  solution  would  depend  upon  the 
proportion  of  active  oxygen  formed  during  the  reaction. 

A  recent  investigator  has,  however,  come  to  the  conclusion 
that  bleaching  is  not  dependent  upon  the  formation  of  oxygen  in 
the  case  of  the  hypochlorites.  He  dissolved  hypochlorites  in  a 
medium  containing  no  oxygen,  and  added  coloured  substances, 
which  he  found  to  be  bleached.  He  came  to  the  conclusion 
that  some  of  the  hydrogen  of  the  substance  to  be  bleached  was 
seized  upon  by  the  chlorine,  forming  hydrochloric  acid,  and 
that  bleaching  was  really  a  process  of  reduction  and  not  of 
oxidation.  This,  however,  has  by  no  means  been  proved  in  the 
case  of  ordinary  solutions  ;  and  I  do  not  think  there  is  sufficient 
reason  to  warrant  us  altering  our  views  on  the  subject.  We 
next  have  to  consider  why  it  is  that  one  solution  bleaches  so 
much  more  rapidly  than  another.  This  appears  to  be  closely 


48 


connected  with  the  work  that  the  chlorine  will  do.  As  a  rule, 
when  the  chlorine  acts  rapidly,  the  amount  required  to  bring 
the  colour  up  is  comparatively  small.  This  has  been  explained 
as  follows : — That  bleaching  is  effected  by  a  bombardment  of 
the  atoms  of  oxygen.  If  the  bombardment  is  active,  the 
atoms  which  compose  the  molecules  of  the  colouring  matter 
are,  as  it  were,  kept  in  motion.  If  the  bombardment  is  slow, 
the  atoms  are  able  to  return  to  a  state  of  rest,  and  before 
they  can  be  set  in  motion  again  a  good « deal  of  work  has  to  be 
expended  by  the  oxygen  molecules  to  overcome  their  inertia. 
This  is  a  somewhat  elaborate  theory.  It  will  perhaps  be  better 
understood  by  the  following  illustration: — By  the  old  method 
of  “  pile-driving  ”  a  heavy  weight  is  lifted  to  a  certain  height  and 
allowed  to  drop.  Every  time  the  weight  falls  the  pile  is  driven 
a  small  distance  into  the  ground.  By  the  more  modern  system 
a  machine  is  used,  which  in  action  is  something  like  a  steam 
hammer  dealing  a  succession  of  rapid  blows  upon  the  head  of  the 
pile.  By  the  old  method  a  good  deal  of  work  is  expended  in 
overcoming  the  inertia,  whereas  by  the  latter  process  the  pile 
is  never  allowed  to  come  to  rest.  It  is  claimed  that  the  economy 
of  the  steam  piledriver  is  due  to  the  fact  that  the  pile  is  always 
kept  in  motion.  It  is  possible  that  a  bleaching  solution  that  is 
rapid  in  its  action  is  economical  also  for  a  similar  reason.  It 
is  possible,  however,  that  ordinary  bleaching  powder  solution  is 
wasteful,  on  account  of  the  chlorine  being  given  off  into  the 
atmosphere. 

Solution  a  during  the  bleaching  did  not  smell  of  chlorine, 
whereas  solution  b  had  a  strong  smell  of  chlorine,  but  c  had 
only  a  very  slight  smell.  But  setting  aside  all  theories,  I  think 
that  my  results,  and  those  of  other  investigators,  are  sufficient  to 
show  that  chlorine  as  a  bleaching  agent  varies  very  much 
according  to  the  state  of  its  combination,  and  I  hope  that  this 
will  cause  others,  who  have  better  opportunities  than  I  have,  to 
study  the  subject  much  more  closely. 

In  my  next  lecture  we  will  go  further  into  this  interesting 
subject.  I  have  left  you  purposely  in  doubt  on  one  or  two 
points ;  1  hope  to  give  you  an  explanation,  which  I  believe  to 
be  a  true  one,  as  to  the  cause  of  these  differences  in  “  bleaching 
efficiencies,”  but  the  extent  of  the  subject  renders  it  impossible 
for  me  to  cover  the  ground  in  one  lecture. 


LECTURE  IV. 


THE  CHEMISTRY  OF  BLEACHING. 

Early  history  of  bleaching — Sun  bleaching — Ozone — The  atmosphere — Its 
bleaching  effect — Sunlight — Hermite  electrolytic  bleaching — “  Still  ” — • 
“Circulating” — Continuous  use  of  bleach  liquor — Temperature  of  bleach 

liquor. 


*It  appears  that  the  Egyptians  and  the  Phoenicians  during 
the  early  ages  were  well  skilled  in  the  art  of  bleaching.  It  is 
stated  in  the  Encyclopedia  Britannica  that  down  to  the 
middle  of  the  eighteenth  century  the  Dutch  possessed  almost  a 
monopoly  of  the  bleaching  trade,  although  mention  is  found  of 
bleach  works  at  Southwark,  near  London,  as  early  as  the  middle 
of  the  seventeenth  century.  It  was  customary  to  send  all  the 
brown  linen,  then  largely  manufactured  in  Scotland,  to  Holland 
to  be  bleached.  It  was  sent  away  in  the  month  of  March  and  not 
returned  till  the  end  of  October,  being  thus  out  of  the  hands 
of  the  merchant  for  more  than  half  a  year. 

The  Dutch  mode  of  bleaching,  which  was  mostly  conducted 
in  the  neighbourhood  of  Haarlem,  was  to  steep  the  linen  first 
in  a  waste  lye,  and  then  for  about  a  week  in  a  potash  lye,  poured 
over  it  boiling  hot.  The  cloth,  being  taken  out  of  this  and 
washed,  was  next  put  into  wooden  vessels  containing  buttermilk, 
in  which  it  lay  under  a  pressure  for  five  or  six  days.  After 
this  it  was  spread  upon  grass,  and  kept  wet  for  several  months, 
exposed  to  the  sunshine  of  the  summer. 

Since  that  time  these  processes  have  gone  through  a  number 
of  evolutionary  changes.  A  boil  in  carbonate  of  soda  has  taken 
the  place  of  the  above-mentioned  alkaline  treatment,  which  was 
known  as  “  bucking.”  A  soak  in  dilute  muriatic  acid  has 
taken  the  place  of  treatment  with  buttermilk,  and  a  treatment 
with  a  weak  solution  of  bleaching  powder,  called  the  “  chemick,” 


*  The  first  portion  of  this  Lecture  is  largely  abstracted  from  an  article  originally 
contributed  to  the  Paper-Maker,  but  now  out  of  print:  “Bleaching:  The  Primitive 
Methods  of  our  Fore-fathers”  (Beadle),  September,  1895. 


50 


lias  superseded  wetting  and  exposure  for  a  long  period  to  the 
sun’s  rays,  the  latter  of  which  was  known  as  “crofting.”  The 
most  recent  development  is  the  Mather  Patent  Open  Bleach 
System,  by  which  the  cloth  is  bleached  on  large  open  rolls  from 
grey  to  white  without  unwinding  in  14  hours.  Although  the 
above  historical  facts  appear  to  have  little  hearing  on  the  bleaching 
of  paper-stock,  a  knowledge  of  the  chemical  action  that  takes  place 
in  these  primitive  methods  of  bleaching  will,  I  believe,  throw 
light  upon  the  whole  question  of  bleaching,  and  assist  us  in 
clearing  up  certain  anomalies  that  appear  to  exist  in  the  behaviour 
of  solutions  of  different  hypochlorites  when  used  for  bleaching. 

This  primitive  bleaching — in  which  the  sun’s  rays  were  called 
into  requisition — was,  and  still  is,  generally  known  to  this  day  as 
sun  bleaching.  It  is  quite  natural  that,  during  the  early  ages, 
the  sun  should  be  made  available  for  this  purpose,  as  by  repeated 
washing  and  hanging  out  to  dry  in  the  sun  of  any  unbleached 
fabric,  the  same  is  found  to  be  very  much  whitened.  The 
chemical  changes  that  take  place  in  sun  bleaching,  like  a  large 
number  of  other  chemical  changes,  can  only  be  wrought  in 
presence  of  moisture.  There  are  only  certain  of  the  sun’s  rays 
that  are  able  to  assist  the  bleaching.  These  are  known  as  actinic 
rays,  and  are  those  rays  that  are  able  to  promote  chemical 
action.  The  action  of  the  sun’s  rays  upon  the  atmosphere 
through  which  it  shines  is  to  produce  two  substances  which 
have  strong  bleaching  properties.  These  two  substances  are 
ozone  and  hydrogen  peroxide.  Ozone  is  a  condensed  form  of 
oxygen,  and  is  being  continually  formed  from  the  oxygen  ever 
present  in  our  atmosphere.  A  molecule  of  oxygen  is  repre¬ 
sented  as  O,,  and  a  molecule  of  ozone  as  0,,. 

Ozone  is  formed  from  oxygen  as  follows  : — 

30,  =  20,. 

Three  molecules  of  oxygen  become  two  molecules  of  ozone. 

Now  ozone  is  a  much  less  stable  body  than  oxygen,  and  its 
molecules  being  in  a  state  of  unstable  equilibrium,  as  it  wei’e,  it 
requires  very  little  toppling  over  to  its  much  more  stable  con¬ 
dition  of  molecular  oxygen.  When  a  coloured  substance,  such 
as  unbleached  cloth,  comes  in  contact  with  ozone  in  the  atmo¬ 
sphere,  this  toppling  over  is  effected,  and  the  ozone  is  transformed 
back  to  oxygen.  Ordinary  oxygen  (molecules  of  oxygen)  is 
unable  to  bleach  ;  but  what  is  knowm  as  “  nascent  ”  oxygen — 
that  is,  oxygen  just  freed  from  its  combination  and  in  its  free 


51 


state — is  able  to  bleach.  Ozone,  by  breaking  down  to  ordinary 
oxygen,  provides  a  source  o£  nascent  oxygen. 

03  =  02  +  O 

Ozone  becomes  ordinary  oxygen  and  nascent  oxygen. 

Hydrogen  peroxide,  the  other  bleaching  constituent  of  our 
atmosphere,  is  also  an  unstable  compound,  and  this,  in  contact 
with  substance  capable  of  being  bleached,  liberates  nascent 
oxygen  and  forms  water. 

Ha02  =  H,0  +  0 

Hydrogen  peroxide  =  water  and  nascent  oxygen. 

Hydrogen  peroxide  and  ozone  tire  often  formed  simul¬ 
taneously.  It  was  generally  believed  that  ozone  was  formed  by 
electrical  discharges  in  the  atmosphere,  but  it  has  been  proved 
that  it  is  invariably  formed  when  water  evaporates,  and  it  is  to 
the  latter  source  we  would  rather  look  for  the  ozone  that  takes 
an  active  part  in  the  bleaching  of  cellulose.  Both  the  above 
bleaching  agents  may  be  expended  uselessly  when  brought  in 
contact  with  substances  to  be  bleached.  Ozone  is,  however, 
reduced  to  ordinary  oxygen  when  in  contact  with  some  organic 
substances.  When  it  is  expended  usefully,  only  one-third  of 
the  ozone  can  oxidise  the  organic  colouring  matter,  the  other  two- 
thirds  going  to  form  ordinary  oxygen. 

0:J  =  02  +  0 

Ozone  =  ordinary  oxygen  and  nascent  oxygen. 

AYhen  it  is  expended  uselessly  by  reduction  in  contact  with 
organic  matter  the  equation  is : — 

208  =  30, 

Hydrogen  peroxide,  when  bleaching,  liberates  one  atom  of 
nascent  oxygen  with  the  formation  of  water. 

HA  =  H20  +  0 

The  economy  and  rapidity  of  the  bleaching  depends  upon 
the  prevention  of  the  reduction  of  ozone  to  ordinary  oxygen, 
and  of  hydrogen  peroxide  to  water  and  ordinary  oxygen.  In 
short,  it  is  necessary  to  ensure  that  the  conditions  are  such 
that  the  liberated  nascent  oxygen  is  made  to  enter  into  com¬ 
bination  with  the  organic  colouring  matter,  with  the  formation  of 
colourless  oxidised  products,  instead  of  being  reduced  to  ordinary 
oxygen. 

Ozone  is  generally  supposed  to  be  more  abundant  during 
sunshine,  and  that  the  absence  of  the  sun's  rays  allows  of  the 
reduction  of  ozone  to  ordinary  oxygen,  especially  in  the  vicinity 
of  crowded  cities,  where  the  issuing  organic  gases  to  a  large 
extent  assist  the  reduction  of  ozone  to  ordinary  oxygen.  The 


heat  rays  emanating  from  the  sun  may  bring  about  the  formation 
of  ozone  by  the  evaporation  of  water,  which  is  supposed  by 
meteorologists  and  chemists  to  be  the  chief  source  of  ozone  in 
the  atmosphere.  The  actinic  rays  from  the  sun  may  change  the 
molecules  of  ordinary  oxygen  into  ozone,  but  this,  as  far  as  I  am 
aware,  has  never  been  proved.  There  can  be  little  doubt,  however, 
that  the  actinic  rays  from  the  sun  are  such  as  to  render  the 
colouring  matter  of  fibres  susceptible  of  attack  by  nascent  oxygen, 
ozone,  or  hydrogen  peroxide.  When  a  cellulose  material,  such 
as  unbleached  rags,  is  spread  out  upon  grass  and  exposed  to  the 
sun’s  rays  during  summer,  it  will  be  found  that  the  material  is 
gradually  bleached ;  it  will  be  found  also  that  the  bleaching  is 
very  much  accelerated  by  periodical  damping  with  water.  We 
must  assume,  first  of  all,  that  hydrogen  peroxide  and  ozone  are 
present  in  an  open  space  where  the  sun  is  shining,  and  that  the 
evaporation  of  water  used  to  damp  the  material  gives  rise  to 
the  formation  of  further  quantities  of  ozone.  The  water  also 
being  a  solvent  for  both  hydrogen  peroxide  and  ozone,  the 
oxidising  agents  are  brought  into  immediate  contact  with  the 
material.  The  production  of  ozone  is  promoted  by  alternations 
of  damp  and  dry  and  hot  and  cold  air.  The  hoar  frosts  and 
morning  dews  also  increase  the  hydroscopic  moisture  of  the 
cellulose,  besides  supplying  a  quantity  of  surplus  moisture  which 
is  evaporated  on  exposure  to  the  sun’s  rays.  Sun  bleaching  was 
never  studied  at  all  in  a  scientific  manner,  as  the  use  of  bleaching 
powder  came  in  long  before  the  chemistry  of  sun  bleaching  began 
to  be  understood.  To  appreciate  how  precarious  this  process  is,  it 
is  necessary  to  have  some  knowledge  of  the  intensity  of  the 
sun’s  rays  at  different  hours  of  the  day  and  at  different  seasons 
of  the  year.  When  the  sun  is  perfectly  perpendicular,  as  in 
equatorial  regions,  the  amount  of  light  intercepted  by  the 
atmosphere  on  a  cloudless  day  amounts  to  16  per  cent,  of  the 
total.  When  the  sun  is  at  an  angle  of  30  degrees  with  the 
horizon  it  has  to  shine  through  the  depth  of  two  atmospheres,  and 
only  70  per  cent,  of  the  total  light  reaches  the  earth.  When 
the  angle  is  20  degrees  only  about  60  per  cent,  reaches  the  earth. 
When  at  an  angle  of  8  degrees  only  one-fifth  the  total  rays  reach 
the  earth ;  and  when  the  sun  is  about  to  set  only  2  per  cent, 
of  the  rays  reach  the  earth.  We  see  then  from  this  that  the 
bleaching  power  of  the  sun’s  rays  is  greatly  diminished  as  it  nears 
the  horizon,  and  as  the  sun  is  nearly  always  at  a  considerable 
angle,  we  get  very  far  short  of  the  maximum  effect  of  the  sun’s 
rays.  Another  point  in  this  connection  is  worthy  of  notice. 


The  rays  intercepted  by  the  atmosphere  are  just  those  that  are 
most  active  in  their  bleaching  effect,  namely,  the  actinic  rays. 
The  other  rays  are  inoperative  in  so  far  as  they  do  not  affect 
the  colouring  matter  to  be  bleached.  The  heat  rays  may  promote 
the  evaporation  of  water  and  so  manufacture  ozone,  but  their 
function  is  probably  small  in  comparison  with  the  actinic 
rays.  At  any  period  during  daylight  some  actinic  rays  reach 
the  earth,  but  these  diminish  much  more  rapidly  with  the 
angularity  of  the  sun  than  do  the  total  rays  that  reach  us.  To 
these  ever-changing  conditions  must  be  added  the  uncertainty 
of  the  weather,  which  makes  sun  bleaching  more  uncertain  even 
than  harvesting.  It  appears  that  grass  or  sun  bleaching  is  less 
destructive  than  hypochlorite  bleaching,  and  on  this  account  it 
is  still  made  use  of  to  a  limited  extent  in  the  textile  trade,  and,  I 
believe,  has  been  seriously  considered  recently  as  a  means  of 
bleaching  rags  for  papermaking. 

In  some  old  text-books  on  papermaking  I  have  seen  it 
stated  that  the  bleach-house  should  be  constructed  with  as  much 
glass  roofing  as  possible,  so  that  the  bleaching  operations  should 
be  assisted  by  the  sun’s  rays.  As  hypochlorite  bleaching  is  so 
much  more  rapid  than  sun  bleaching,  the  latter  can  be  of  very 
little  service  in  conjunction  with  the  former.  The  old  method 
of  rendering  raw  material  white  before  the  introduction  of  the 
modern  methods  of  boiling  and  bleaching  may  be  of  interest  and 
throw  some  light  on  the  subject.  This  is  my  onlv  reason  for 
describing  these  obsolete  methods.  In  ancient  days  the  sorted 
rags  were  well  wetted  with  water  and  heaped  up  for  several 
weeks  until  they  got  thoroughly  warmed  in  the  centre.  They 
were  occasionally  turned  to  prevent  superheating  and,  con¬ 
sequently,  spontaneous  combustion,  which  might  subsequently 
ensue.  By  means  of  the  above  process  the  non-cellulose,  which 
included  resinous  matter,  oily  matter,  organic  dirt,  &c.,  was  more 
readily  oxidised  than  the  cellulose,  and  consequently  converted 
into  soluble  products  that  could  be  readily  removed  by  subsequent 
washing.  There  is  much  danger  of  tendering  the  fibre  by  con¬ 
version  into  oxycellulose,  and  in  the  presence  of  nitrogenous 
substances  such  as  gelatine  this  change  appears  to  be  much  more 
rapid.  Even  with  fairly  pure  fibre  a  mould  is  very  readily  formed. 
With  bleached  half-stuff  that  has  been  allowed  to  remain  in  large 
lumps  for  a  time  in  a  cool,  damp  place,  a  black  mould  is  often 
developed,  which,  if  allowed  to  spread,  does  considerable 
destruction  to  the  cellulose. 

After  the  rags  had  been  submitted  to  the  above  process, 


54 


which  took  the  place  of  our  modern  process  of  boiling  with 
alkali  under  pressure,  they  were,  after  thorough  washing  to 
remove  the  soluble  products,  spread  out  on  grass  in  the  sun  and 
occasionally  damped  with  water  until  they  were  thought  to  be 
sufficiently  bleached  for  what  then  took  the  place  of  our 
hollander.  The  beating  operation  was  generally  done  in  a  large 
mortar,  into  which  a  large  pestle  was  made  to  drop  by  means 
of  a  crank.  The  treatment  that  the  rags  here  received  was 
equivalent  to  what  might  be  got  by  stamping  rags  to  pieces  in 
water  with  an  ordinary  pestle  and  mortar. 

As  far  as  I  know,  there  was  no  washing  process  during  the 
disintegration  of  the  fibre.  The  cleansing  of  the  material 
depended  entirely  upon  the  heaping  up  or  tendering  process  and 
the  sun  bleaching  and  their  attendant  washings.  It  appears  that 
a  large  portion  of  the  cellulose  was  not  affected  by  the  tendering 
process,  although  the  fabric  came  to  pieces  more  readily.  The 
papers  made  befoi’e  the  introduction  of  chemicals  have  stood 
wonderfully  well,  and  whatever  objections  may  be  raised  against 
these  primitive  processes,  the  net  result  was  good,  and  it  appears 
that  the  rags  were  purified  and  converted  into  paper  with  a 
minimum  effect  upon  the  cellulose  itself.  It  appears,  at  any 
rate,  that  the  cellulose  finding  its  way  into  the  finished  paper 
was  remarkably  inert  to  atmospheric  influences.  This  is  un¬ 
doubtedly  largely  due  to  the  fact  that  the  papers  were  free  from 
the  residue  of  chemicals  which  is  to  be  found  in  all  papers  the 
fibres  of  which  have  been  submitted  to  chemical  treatment.  These 
methods  had  been  greatly  improved  if  they  had  been  studied 
in  a  scientific  manner  by  papermakers.  In  the  light  of  our 
present  knowledge,  great  advances  might  yet  be  made  in  this 
direction.  The  great  objection  to  these  processes  is  the  time 
required.  They  took  as  many  months  as  our  present  methods 
do  hours.  With  a  warm  solution  of  a  hypochlorite  and  a  gentle 
circulation  of  the  liquor,  as  much  bleaching  can  be  effected  in 
one  hour  as  is  possible  in  one  month  in  summer  with  a  good  sun. 
With  the  discovery  of  chlorine  and  its  bleaching  power,  and  the 
subsequent  discovery  of  calcium  hypochlorite  or  bleaching  powder 
as  a  bleaching  agent,  sun  bleaching  was  rapidly  abandoned.  The 
chemistry  of  sun  bleaching  is  very  closely  allied  to  the  chemistry 
of  hypochlorite  bleaching :  the  active  principle  is  the  same.  I 
have  given  a  general  outline  of  these  antiquated  and  obsolete 
methods  not  because  they  are  likely  to  be  of  any  particular  value 
in  themselves,  but  because  I  feel  that  some  knowledge  of  them 
is  necessary  in  preparation  of  what  is  to  follow. 


55 


We  referred  briefly  in  our  last  lecture  to  the  Hermite 
bleaching  solution,  got  by  electrolysing  a  solution  of  magnesium 
chloride. 

As  far  as  I  am  aware  there  are  no  published  results  of 
experiments  upon  the  bleaching  efficiency  of  the  Hermite  bleach¬ 
ing  solution  in  comparison  with  that  of  a  solution  of  bleaching 
powder  upon  the  bleaching  of  cotton  and  linen  fibre.  All  the 
published  results,  viz.,  those  of  Messrs.  Cross  &  Sevan  and 
Professor  Pictet,  are,  I  believe,  upon  the  bleaching  of  wood  pulp. 

I  have  made  a  series  of  experiments  to  determine  whether  the 
Hermite  solution  still  gave  the  same  efficiency  when  used  for 
bleaching  cotton  and  linen  rags  and  rag  half-stuff.  These  results 
were  published  in  the  Chemical  News.  Eor  the  purpose  of  these 
trials  a  small  beater  was  used,  similar  in  construction  to  the  paper- 
maker’s  hollander. 

I  took  half- stuff  produced  from  second  quality  linen  rags  and 
from  second  quality  cotton  rags.  Before  doing  experiments  in 
the  small  beater,  I  mixed  a  known  weight  of  each  of  the  half-stuffs 
with  a  carefully  ascertained  volume  of  Hermite  solution,  also 
with  bleaching-powder  solution,  the  chlorine  strength  of  each 
having  been  carefully  ascertained. 

The  time  required  to  bleach  the  materials  to  a  full  white  was 
noted,  and  when  the  bleaching  was  complete  the  available  chlorine 
in  the  residual  liquors  was  determined,  and  the  amount  of  chlorine 
consumed  by  the  fibre  calculated. 

The  following  are  the  results  :  — 


Put  in 

-G  9* 

^2 

Half  Stuff. 

Dry 

Weight. 

Grms. 

Liquor. 

1>  .  u, 

CC  A 

S  - 

O 

1.  Linen 

162.6 

Hermite 

3.8 

17.2 

2.  „ 

162.6 

Bleaching  Powder 

3.16 

19.4 

3.  Cotton 

176.2 

Hermite 

2.8 

15.9 

4.  „ 

176.2 

Bleaching  Powder 

3.16 

18.0 

Consumed  : — 


Chlorine. 

Grammes. 

Chlorine  per  cent, 
on  fibre. 

Time  of  bleaching. 

1 

2.44 

1.5 

30  minutes. 

2 

3.72 

2.29 

4  hours. 

O 

o 

4.0 

2.27 

2 

4 

6.49 

3.68 

10  „ 

56 


The  efficiency  of  chlorine  in  the  Hermite  liquid  as  compared 
with  that  of  chlorine  in  ordinary  bleaching  powder  is  claimed 
by  the  inventors  to  be  as  5  is  to  3.  This  has  been  substantiated 
by  the  results  of  Messrs.  Cross  &  Bevan  and  Professor  Pictet. 

3  :  5  :  :  1  :  1.66 

Comparing  this  with  the  experiments  above  — 


Hermite. 

Bleaching  Powder. 

1  and  2 

1.5 

:  2.35  : 

:  1  :  1.54 

3  and  4 

2.27 

:  3.68  : 

:  1  :  1.65 

These  results,  therefore,  confirm  fairly  closely  those  of  other 
observers.  The  next  two  experiments  were  done  with  a  view  of 
finding  how  long  the  Hermite  solution  took  to  exhaust  itself  if  the 
chlorine  put  in  was  the  exact  amount  necessary,  according  to 
the  above  experiments,  to  do  the  bleaching. 

The  rate  of  bleaching  was  much  slower  than  if  the  chlorine 
had  been  used  greatly  in  excess.  After  three  days,  however,  the 
liquid  only  contained  the  least  possible  trace  of  chlorine,  and  the 
fibre  appeared  to  be  perfectly  bleached. 

The  preceding  experiments  were  all  done  with  “  still  ”  liquor. 
In  the  following  experiments  the  half-stuff  was  put  into  the 
small  beater  and  the  Hermite  liquor  allowed  to  flow  round  the 
beater,  and  was  washed  out  again  by  means  of  a  washing  drum, 
from  whence  it  was  delivered  to  a  store  tank  and  then  again  to 
the  beater.  The  total  amount  of  liquor  was  first  of  all  measured 
both  into  the  beater  and  into  the  store  tank,  from  which  a  sample 
was  taken  and  tested  for  chlorine.  This  experiment  was  not  done 
under  the  most  favourable  circumstances,  as  the  liquor  was  drawn 
from  the  store  tank  and  not  from  the  electrolysing  tank  whilst 
the  electrolysis  was  going  on,  which  I  think  would  have  made  a 
considerable  difference  to  the  results. 

Put  in  : — 


Half-Stuff. 

Weight 
Dry  Fibre. 
Grms. 

Volume 

of 

Liquid. 

Strength 
per  Litre. 
Grms. 

Per  Cent, 
on 

Fibre. 

Linen 

542 

56-12 

2.64 

27.3 

Cotton  .  . 

470 

56-12 

2.64 

31.5 

57 


Consumed  :  — 


Weight  of  Chlorine. 

Per  Cent,  on  Fibre. 

Time. 

5.6 

1.03 

40  minutes. 

5.6 

1.20 

60  „ 

It  is  evident  that  the  circulating  liquor  is  more  economical 
than  the  non-circulating. 


Half-Stuff. 

Non¬ 

circulating 

Chlorine 

Consumed. 

Circulating 

Chlorine 

Consumed. 

Saving  by 
Circulating  over 
Non-circulating. 

Linen  .  . 

1.5 

1.03 

30  per  cent. 

Cotton  .  . 

2.27 

1.20 

47  „ 

My  results  confirm  those  of  other  observers  as  regards  the 
rapidity  of  bleaching  by  the  Hermite  solution,  which  I  found  to 
bleach  very  rapidly,  doing  as  much  work  in  thirty  minutes  as 
bleaching  powder  solution  of  the  same  strength  would  do  in  three 
hours. 

I  also  found  that  Hermite  solution  will  bleach  in  one 
treatment :  in  some  instances  where  any  amount  of  bleaching 
powder  will  fail  to  do  so  without  an  intermediate  acid  treatment. 
The  solution  can  be  used  either  circulating  or  stored  in  tanks  for 
use  like  ordinary  bleaching  powder  solution,  but  the  latter,  as  we 
have  seen,  does  not  give  such  good  results. 

If  it  were  not  for  practical  difficulties  in  regard  to  the 
production  of  the  electrolysed  solution,  the  Hermite  liquor  might 
have  proved  a  great  success.  It  was  never  successfully  installed 
in  any  mill  in  this  country,  although  it  was  in  operation  in 
France.  The  necessity  of  having  to  return  the  liquor  from  the 
potcher  to  the  electrolysing  tank  to  be  revivified  went  very  much 
against  it.  If  any  electrolysed  solution  is  to  become  a  practical 
success  it  must  be  of  such  a  nature  that  weak  solutions  can  be 
completely  and  economically  electrolysed,  so  that  when  the 
bleaching  is  accomplished  the  spent  liquor  can  be  thrown  away 
without  loss.  This  neither  the  Hermite  nor  the  Andrioli  solu¬ 
tions  were  able  to  fulfil. 


58 


After  having  gone  into  the  theoretical  aspect  ol  the  chemistry 
of  bleaching,  we  will  now  go  to  consider  the  more  practical  details. 

Boiled  rags  were  formerly  bleached  in  the  old-fashioned 
tumblers,  but  for  many  years  now  some  mills  have  bleached  the 
rags  by  piling  them  up  in  chambers  and  promoting  the  circulation 
of  warm  bleach  through  the  mass,  much  on  the  same  principle  as 
that  of  a  vomiting  boiler,  but  taking  care  that  the  temperature 
does  not  rise  above  95°  Fahr.  The  rags  are  not  disturbed  during 
the  treatment,  but  the  liquor  is  in  constant  circulation  through 
the  mass,  and  the  action  is  very  rapid  and  produces  a  very  good 
colour.  The  liquor  is  immediately  drained  off.  If  the  rags  are 
at  once  transferred  to  the  beaters  after  douching  them  with  cold 
water  there  is  no  fear  of  injury,  but  if  left  piled  up  in  a  warm  con¬ 
dition  the  centre  of  the  mass  undergoes  a  most  curious  change. 
On  turning  the  mass  over  for  its  removal  to  the  beaters  after, 
say,  a  fortnight,  or  even  after  a  few  days,  we  notice  a  sweet 
beeswax-like  smell.  Whilst  the  rags  are  being  broken  in,  if  you 
look  along  the  surface  of  the  water  after  it  leaves  the  back  fall, 
a  thin  film  is  often  noticed.  If  much  of  these  rags  is  used  in 
the  breaker  the  surface  of  the  latter  is  soon  coated  with  a  thin 
wax-like  film,  which  can  easily  be  scraped  off.  This  film  has  been 
submitted  to  careful  examination.  It  may  become  a  source  of 
constant  annoyance  by  breaking  off  and  finding  its  way  into  the 
paper.  Under  these  conditions  of  hot  bleaching,  instead  of  the 
bleach  converting  the  cellulose  into  oxycellulose,  it  undergoes  a 
fatty  degeneration  by  slow  conversion  into  a  waxy  substance, 
which,  by  treatment  with  alkali,  is  easily  saponified  and  converted 
into  a  soap.  This  action  occasionally  occurs,  giving  rise  to  the 
so-called  waxes  and  rosins,  and  is  certainly  a  drawback  to  this 
form  of  hot  bleaching,  and  may  result  also  when  stuff  is  bleached 
hot  in  the  bleacher  and  allowed  to  drain  without  cooling. 

The  advantages  of  the  above  method  are  its  great  rapidity 
as  compared  with  cold  bleach ;  it  is  performed  with  a  minimum 
quantity  of  liquor,  so  that  the  chlorine  can  be  used  at  its  maximum 
strength  ;  it  can  be  applied  to  the  rags  without  their  being  tumbled 
about.  It  Is  somewhat  difficult  to  ensure  even  penetration.  The 
method,  I  believe,  has  been  in  vogue  for  many  years,  but  it  is 
difficult  to  maintain  a  uniform  temperature  without  careful 
attention. 

The  liquid  which  drains  away  from  rag-bleaching  should,  in 
my  opinion,  not  be  used  again  on  another  batch,  as  it  acts  upon 
and  tends  to  exhaust  a  fresh  solution.  It  is  sometimes  used  again 
for  the  purpose  of  economising,  but  it  is  more  likely  to  result  in 


59 


waste.  I  cannot  say  that  this  remark  applies  to  the  bleaching 
of  esparto  where  the  process  is  carried  on  continuously,  the  bleach 
passing  in  one  direction  and  the  bleached  material  in  the  other. 

Those  of  you  who  are  chemists  can  easily  verify  my  statements 
by  mixing  some  fresh  bleach  of  known  chlorine  strength  with 
some  spent  bleach  liquor  which  has  been  used  several  times.  You 
can  ascertain  the  effect  of  the  spent  liquor  upon  the  fresh  bleach 
solution  by  testing  it  periodically.  You  will  notice  a  steady 
falling-off,  especially  if  the  solution  is  kept  warm.  This  falling- 
off  must  take  place  in  a  like  manner  when  spent  or  partly  spent 
liquor  is  revivified  by  the  addition  of  more  bleach.  In  the  case  of 
esparto  it  may  be  different  when  the  bleach  solution  is  kept  strong 
and  working  continuously.  The  process  has  to  be  conducted 
quickly  and  necessitates  a  strong  liquor,  and  to  throw  this  away 
still  containing  a  lot  of  bleach,  would  be  less  economical  than  using- 
liquor  over  again,  although  in  the  latter  case  waste  is  going  on 
through  by-products  from  previous  bleacbings  destroying  the 
chlorine. 

There  is  one  great  danger  with  circulating  hot  bleach  through 
stationary  rags.  When  an  attempt  is  made  to  bleach  iron 
mordanted  coloured  rags,  ferric  oxide  or  magnetic  oxide  of  iron  is 
formed  in  situ.  Tinder  ordinary  circumstances,  bleach  powder  does 
not  act  deleteriously  upon  cellulose,  but  it  is  liable  to  do  so  when 
hot.  In  the  presence,  however,  of  oxide  of  iron,  instead  of 
bleaching  the  colour,  the  oxide  acts  as  a  conveyer  of  oxygen  from 
the  bleach  to  the  cellulose  in  such  a  way  as  to  tender  it.  The 
oxygen  is  supplied  by  the  decomposition  of  the  bleach  to  the 
ferric  oxide,  which  in  turn  conveys  it  to  the  cellulose  and  converts 
it  into  oxycellulose. 

The  reduced  iron  is  again  oxidised  by  the  bleach,  and  then 
the  process  is  repeated,  with  the  result  that  the  rag  is  tendered 
instead  of  being  bleached.  I  have  seen  iron  mordanted  rags  mixed 
with  other  rags,  the  mordanted  ones  completely  tendered,  and  the 
rest  bleached  but  otherwise  unaffected,  both  having  undergone 
the  same  treatment. 

I  want  you  to  realise  that  this  method  of  hot  circulation 
allows  the  air  as  well  as  the  bleach  to  come  into  direct  contact 
with  the  material  to  be  bleached  ;  whereas  in  the  method  of  circu¬ 
lation  about  to  be  discussed,  the  bleaching  is  done  by  total 
immersion  in  the  liquid,  except  at  the  surface  of  the  stuff. 

Let  us  now  consider  another  set  of  conditions  when  liquor  in 
the  potcher  is  circulating  whilst  the  bleaching  is  being  carried  on. 
The  circulation  is  a  valuable  aid  to  bleaching,  as  it  promotes  the 


CO 


chemical  action  in  various  ways.  It  reduces  the  time  of  treatment, 
and  tends  to  make  the  treatment  much  more  uniform  than  it 
would  otherwise  be,  such  as  in  the  steeping  tank  bleach. 

In  the  bleaching  of  some  stuffs,  such  as  esparto,  where  the 
mass  is  kept  in  circulation,  and  where  it  is  expedient  to  make 
the  process  as  rapid  and  continuous  as  possible,  I  venture  to  think 
there  must  be  considerable  saving  of  time  effected,  due  to  the 
fact  of  keeping  the  stuff  in  motion.  There  can  be  no  harm  or 
danger  to  the  material  in  rapidly  agitating  it  or  keeping  it  in 
motion  during  the  time  the  bleach  is  acting.  Such  agitation 
results  in  economy  of  bleach  as  well  as  saving  of  time.  This  I 
have  shown  by  actual  figures  to  be  true  of  the  Hermite  solution, 
but  it  is  equally  true  of  solutions  of  ordinary  bleaching  power 
whether  hot  or  cold.  It  is  necessary  to  take  into  consideration 
the  cost  of  keeping  the  stuff  in  motion,  which  may  amount  to 
more  than  the  saving  in  bleaching  powder.  Apart  from  this,  time 
is  an  important  factor,  and  anything  that  will  help  to  get  the 
stuff  out  of  hand  quickly  is  to  be  welcomed. 

As  will  be  seen  hereafter,  agitation  not  only  accelerates  the 
rapidity  of  the  bleaching,  but  it  also  in  a  measure  brings  into 
play  a  somewhat  different  chemical  reaction.  The  probability  is 
that  the  nascent  oxygen  is  much  more  effective,  and  that  less  of 
it  is  converted  into  ordinary  oxygen  or  able  to  act  on  bleach 
products  already  formed. 

It  is  easier  and  safer  to  apply  heat  when  the  stuff  is  properly 
agitated.  Of  course  the  temperature  is  rising  from  the  very  com¬ 
mencement,  due  to  the  rapid  agitation,  but  as  chemical  reactions  of 
this  kind  are  not  influenced  so  much  at  a  low  temperature  as  at  a 
high  one,  every  degree  of  rise  of  temperature,  say  between  80° 
and  90°  Tahr.,  promotes  a  greater  increase  of  chemical  energy 
than  each  degree  of  rise  between  50°  and  60°  Tahr.,  consequently 
the  energy  of  the  bleaching  due  to  increased  temperature  is 
more  marked  after  the  agitation  is  conducted  for  some  time. 
There  is  little  or  no  benefit  in  warming  the  stuff  through  a  few 
degrees  only.  The  real  benefit  is  derived  when  the  stuff  is  raised 
to  its  safe  limit,  but  this  safe  limit  should  on  no  account  be 
exceeded. 

It  can  hardly  be  claimed  that  any  mechanical  cleansing  can 
be  effected  while  the  bleaching  is  actually  going  on,  but  extraneous 
matter  and  dirt,  after  the  bleach  has  acted  upon  it,  may  become 
loosened  and  detached.  This  loosening  may  be  assisted  by 
mechanical  agitation,  but  the  dirt  cannot  be  got  away  until  the 
bleach  is  washed  out. 


G1 


We  have  already  referred  to  the  theoretical  action  of  bleach¬ 
ing  powder,  and  endeavoured  to  explain  it  on  the  assumption  that 
ozone  is  formed,  but  there  is  no  reason  for  supposing  that  ozone 
alone  or  in  conjunction  with  one  of  the  hypochlorites  cannot  be 
used  to  great  advantage  in  the  bleaching  of  paper  stock.  If  ozone 
is  ever  to  come  into  commercial  use  for  bleaching,  its  manufacture 
will  have  to  be  much  cheapened  and  simplified.  Of  this  there 
seems  little  prospect  in  the  near  future.  Ozone  by  itself  is  a 
powerful  bleaching  agent,  and  is  likely  to  come  into  commercial 
use  as  such  if  a  cheap  enough  method  can  be  devised  of  making 
it.  Ozone,  furthermore,  accelerates  the  action  of  bleaching 
powder  and  results  in  a  saving  of  chlorine.  The  presence  of 
ozone  and  peroxide  of  hydrogen  in  the  air  lashed  into  the  stuff  by 
the  action  of  the  beater-roll  must,  in  a  measure,  affect  the  rapidity 
as  well  as  the  economy  of  bleaching,  but  to  what  extent  it  is 
not  easy  to  ascertain.  I  have  heard  of  cylinders  of  com¬ 
pressed  oxygen  being  used  in  conjunction  with  bleaching  powder 
in  the  potcher,  but  have  had  no  experience  of  its  use. 

The  presence  of  direct  sunlight  in  a  bleach-house  must  also- 
assist  the  bleaching,  and  more  so  when  the  stuff  is  agitated, 
continually  exposing  to  the  sun's  rays  fresh  layers  of  pulp. 

It  is  most  essential  when  bleaching  with  hot  liquor  to  avoid 
over-heating.  It  is  often  the  practice  to  have  live  steam  in  the 
potcher  to  raise  the  stuff  to  the  necessary  temperature. 

Care  must  be  taken  that  where  the  steam  enters  the  potcher 
there  should  not  be  local  heating.  This  is  liable  to  take  place  if 
the  potcher  circulates  slowly.  It  is  an  extremely  dangerous 
thing  to  rely  on  a  man’s  judgment  as  to  the  temperature.  If 
he  passes  his  hand  into  the  stuff  and  thinks  it  is  hot  enough, 
he  may  be  misled,  because  the  apparent  temperature  of  the 
liquid  would  depend  upon  the  temperature  of  the  air  at  the 
time.  A  solution  at  say  80°  Fahr.  would,  for  example,  feel 
cool  in  the  heat  of  summer  but  hot  on  a  winter  morning,  but  the 
chemical  effect  would  be  the  same  summer  or  winter.  The  only 
way  is  to  use  the  thermometer.  The  safest  plan  is  to  heat 
the  potcher  up  to  the'  required  temperature  before  the  addition 
of  any  bleaching  liquor,  and  care  should  be  taken  that  the  steam 
valve  does  not  leak,  or  the  temperature  will  be  further  raised. 
For  straw  and  esparto  the  maximum  should  be  100°  Fahr.,  but 
I  would  suggest  where  it  is  possible  90°-9oo  should  be  the 
maximum.  In  the  case  of  wood,  90°  only  should  be  made  the 
maximum  temperature. 


62 


The  actual  amount  of  chlorine  consumed  in  bleaching  is 
largely  dependent  upon  the  temperature  of  the  stuff.  If  the 
temperature  is  too  high  the  chlorine  consumed  may  be  very  high 
also,  and  the  fibre  at  the  same  time  will  probably  be  injured.  The 
fact  is  that  to  do  the  bleaching  in  a  very  limited  time  in  the  cold, 
a  greater  amount  of  bleach  would  have  to  be  present  than  if  the 
stuff  was  warmed,  on  account  of  the  comparative  slowness  of  the 
cold  bleaching.  Supposing,  for  the  sake  of  argument,  we  required 
20  lbs.  of  bleach  to  do  a  given  amount  of  bleaching  in  two  hours 
in  the  cold,  and  15  lbs.  to  do  the  same  at  90°  Fahr.  At  the  end 
of  the  time  we  might  find  that  the  cold  liquor  contained  the 
equivalent  of  10  lbs.  unconsumed,  and  the  hot  liquor  3  lbs. 
Although  we  should  have  been  compelled  to  add  more  liquor  for 
the  cold  bleach,  yet  the  amount  actually  consumed  would  be  most 
in  the  case  of  the  hot  bleach.  If,  however,  in  the  one  case  we 
bleached  in  the  hot  with  such  quantity  that  the  whole  is  con¬ 
sumed  at  the  end  of  the  bleaching,  and  in  the  other  case  used  a 
cold  solution  which  just  exhausted  itself,  we  should  find  that  the 
hot  bleach  would  consume  from  20  to  50  per  cent,  more  bleach¬ 
ing  powder  than  the  cold  solution. 

In  making  the  above  remarks  I  do  not  wish  to  suggest  that 
this  rule  would  hold  good  in  all  cases.  It  is  true  in  some  cases, 
although  perhaps  not  in  others. 

We  shall  have  to  leave  a  number  of  questions  untouched.  To 
attempt  to  propound  a  theory  to  account  for  the  bleaching  action 
of  different  liquids  is  a  difficult  and  dangerous  task.  I  am  afraid 
I  have  already  trespassed  too  far  in  this  direction.  I  have 
purposely  omitted  all  common  stock  knowledge  such  as  text-books 
give  as  far  as  possible,  and  have  trespassed  on  more  debatable 
ground  in  the  hope  that  young  papermakers  and  chemists  who 
take  an  interest  in  this  subject  may  be  inspired  to  go  further  and 
to  test  the  validity  of  these  remarks  for  themselves. 


LECTURE  V. 


THE  INFLUENCES  OF  MOISTURE  ON  PAPER. 

Effects  of  heat — Expansion  and  contraction  of  cellulose  with  change  of 
moisture — “Sensible”  moisture — The  curling  of  paper  with  change  of 
moisture — Testing  for  “  machine  ”  and  “  cross  ”  direction  by  means  of 
clamping — Effects  of  damping. 


It  is  a  matter  of  common  observation  with  all  of  us  when 
reading  a  book  in  the  scorching  sun  or  close  to  a  blazing  fire,, 
that  the  leaves  and  often  the  cover  become  bent  and  warped  so 
that  the  book  will  not  shut  properly.  If  a  book  is  left  open  in 
the  sun  the  leaves  on  either  side  will  curl  up  and  it  will  be  found 
that  the  uppermost  leaves  are  the  most  curled,  and  often  the 
bottom  ones  remain  quite  flat.  When  the  rays  of  the  sun  meet 
the  paper  it  becomes  heated  on  the  upper  side,  and  some  of  the 
air-dry  moisture  is  driven  off  by  the  heat.  With  almost  all 
substances  heat  expands  them,  but  with  cellulose  and  like  sub¬ 
stances — which  have  the  power  of  abstracting  the  moisture  from 
the  atmosphere  and  giving  the  same  up  when  heated — heat  has 
the  opposite  effect.  Heat  only  has  this  effect  by  reason  of  it 
removing  the  moisture  or  dehydrating  the  cellulose.  It  is  quite 
possible  that  if  a  paper  would  be  -kept  bone  dry,  say,  by  placing 
it  in  an  atmosphere  over  sulphuric  acid  and  gradually  raised  in 
temperature  when  in  this  condition,  that  it  would  show  a  slight 
expansion  with  heat.  This  is  not  a  practical  question,  however, 
for  us,  as  under  all  ordinary  conditions  any  rise  in  temperature 
means  loss  of  moisture  and  consequent  contraction. 

Vegetable  fibres  vary  in  size  according  to  the  amount  of 
moisture  they  contain.  On  a  dry  day  the  ultimate  fibres,  say  of 
cotton,  are  considerably  smaller,  both  in  diameter  and  length,  than 
on  a  damp  day,  and  when  these  fibres  are  immersed  in  water 
they  become  larger.  Cotton  cellulose  in  a  normal  atmosphere 
will  contain  about  7  per  cent,  of  water.  Supposing  we  have  a 
paper  composed  of  cotton  fibres  and  expose  it  to  the  rays  of  the 
sun  the  moisture  will  fall  from,  say,  7  per  cent,  to  5^  per  cent.. 


64 


or  even  4  per  cent.  .  This  fall  brings  about  a  corresponding 
shrinkage  in  the  paper.  If,  now,  we  take  the  paper  into  a  cool, 
shady  place,  the  paper  will  absorb  moisture  until  it  contains  7  per 
cent,  again,  and  will  also  return  to  its  former  size.  Expose  it  on 
a  damp  day  and  its  moisture  may  rise  as  high  as  9  per  cent.,  or 
even  10  per  cent.,  when  it  will  feel  flimsy  and  sensibly  damp.  If 
we  go  further  and  expose  it  all  night  to  the  heavy  dew,  as  some 
of  you  no  doubt  have  observed,  it  will  often  be  covered  with  beads 
of  moisture  when  the  surrounding  objects  are  comparatively  dry. 
Now  take  air-dry  paper  and  lay  it  close  to  a  lire  for  a  few 
minutes,  at  a  temperature  sufficient  to  scorch  the  hand,  it  will 
be  found  that  the  paper  has  further  shrunk,  and  also  that  it  has 
lost  a  great  deal  of  its  flexibility.  This  time  the  paper  has  lost 
nearly  the  wdiole  of  its  atmospheric  or  air-dry  moisture.  It  will 
be  noticed  that  the  paper  has  curled  in  the  direction  of  the  fire. 
If  now  the  paper  be  turned  round  when  about  half  dry  the  paper 
will  uncurl,  and  recurl  only  in  the  opposite  direction.  Whilst 
drying,  it  will  often  be  noticed  that  the  paper  steams  and  des'elops 
a  dampness.  This  is  due  to  the  air-dry  moisture  separating  from 
the  cellulose  before  it  is  able  to  escape  into  the  air,  and  remaining 
on  the  surface  of  the  fibres  as  a  film  of  water. 

The  condition,  as  regards  dampness  or  dryness,  is  a  matter  of 
everyday  observation  with  the  housewife  in  regard  to  household 
linen.  Well-aired  sheets  still  contain  about  7  per  cent,  air-dry 
moisture.  The  reason  that  they  are  safe  even  with  this  amount 
of  moisture  is  that  at  7  per  cent,  the  moisture  is  not  “  sensible 
moisture,”  or  appreciable  to  the  sense  of  touch  or  feel.  When 
the  moisture  is  sufficient  to  become  apparent  to  the  touch,  the 
linen,  through  the  presence  of  what  we  may  regard  as  excess  of 
moisture,  becomes  conductive  of  heat  and  conducts  the  heat  away 
from  the  body,  whereas  well-aired  linen  is  an  insulator  of  heat  and 
consequently  prevents  the  heat  of  the  body  from  escaping. 
Hence  the  danger  of  damp  linen  and  the  necessity  for  well  airing. 
With  paper  also  the  moisture  only  becomes  apparent  to  our  senses 
( i.e .,  feels  damp)  when  it  exceeds  a  certain  amount,  and  this 
amount  would  be  greater  in  a  wood  paper  than  in  a  rag  paper. 
Although  our  senses  only  reveal  the  excess  moisture,  the  cellulose 
or  fibres  of  which  the  paper  is  composed  is  much  more  sensitive, 
and  in  proportion  as  it  yields  up  moisture  below  its  air-dry  state, 
it  becomes  more  harsh  and  resistent  and  even  brittle,  and  loses 
much  of  its  useful  qualities.  It  is  a  fortunate  provision  of  nature 
that  the  ordinary  air-dry  state  is  that  state  which  shows  up  fibres 
to  their  best  advantage  for  papermaking. 


65 


Take  a  sheet  of  paper  and  breathe  on  it,  it  will  have  the 
opposite  effect  to  placing  it  before  the  fire.  The  edges  of  the 
paper  will  have  curled  away  from  the  surface  breathed  upon. 
This  is  due  to  the  fact  that  the  breath  is  charged  with  moisture, 
which  is  imparted  to  the  surface  breathed  upon,  which,  in 
consequence,  expands  and  forms  the  convex  surface  of  the  curve. 
The  heat  of  the  fire  contracts  the  surface  nearest  to  it  by  the 
removal  of  water,  and  in  consequence  of  it  being  less  in  area  than 
the  unheated  surface,  forms  the  concave  surface  of  the  curve. 
It  should  be  noticed,  therefore,  that  most,  if  not  all  papers  under 
ordinary  atmospheric  conditions  are  susceptible  to  heat  and 
moisture.  If  heated  they  contract  and  if  moistened  they  expand, 
and  if  either  of  these  processes  is  applied  to  one  surface  only,  or 
more  to  one  surface  than  the  other,  the  paper  is  bound  to  curl. 

When  water  is  applied  rapidly  to  one  surface  of  a  sti'ip  of 
paper  with  a  brush,  it  often  lifts  itself  up  from  the  surface  on 
which  it  is  placed,  forming  an  arch  supported  at  its  two  ends.  The 
application  of  water  has  the  same  effect  as  breathing  on  the  surface, 
only  it  is  much  more  intense. 

The  curve  that  a  strip  of  a  given  length  makes  on  being 
wetted  on  one  surface  only  depends  largely  upon  the  thickness  of 
the  paper,  and  how  the  paper  is  supported.  It  should  be  noted 
that  this  curling  does  not  take  place  with  an  unsized  paper,  except 
in  a  mild  degree.  A  hard-sized  paper  is  needed  to  show  the  result 
properly.  The  reason  is  that  the  water  so  soon  permeates  an 
unsized  paper,  and  expands  the  other  surface  also. 

If  the  paper  is  free  to  move,  I  have  always  found  the  curve 
to  be  the  arc  of  a  circle.  When  the  paper  is  thin  the  curve  is  the 
arc  of  a  small  circle,  and  when  the  paper  is  thick  the  curve  is  the 
arc  of  a  large  circle.  The  reason  for  this  is  not  far  to  seek. 
When  water  is  applied  to  the  surface  of  a  paper  it  becomes 
expanded  by  a  definite  amount  on  the  wetted  surface.  It  might 
be  2  per  cent.  In  other  words,  if  the  length  of  the  dry  side  was 
represented  by  100,  the  length  of  the  wetted  side  would  be 
represented  by  102.  A  simple  figure  on  the  blackboard  can  be 
drawn  to  show  this  graphically.  The  wetted  surface  is  shown  as 
a  thick  line.  If  nothing  prevented  the  free  expansion  of  the 
wetted  surface,  and  the  dry  surface  resisted  all  expansion,  the  two 
surfaces  would  be  represented  in  section  by  the  arcs  of  two 
concentric  circles,  whose  distance  from  each  other  is  that  of  the 
thickness  of  the  paper.  By  joining  the  two  ends  and  extending 
the  straight  lines  inwards,  the  point  at  which  these  bisect  is  the 
centre  of  the  circle  of  which  the  curved  paper  is  the  arc. 


c 


66 


The  radius  of  the  circle  formed  can  easily  be  measured  by 
tracing  the  curves  on  a  piece  of  paper — drawing  two  lines  at 
tangents  to  the  curve  at  any  two  points,  for  accuracy’s  sake  as  far 
apart  as  the  length  of  curve  will  stand,  and  then  drawing  two 
lines  at  right  angles  to  these  inwards.  The  point  at  which  these 
lines  meet  is  the  centre  of  the  circle.  It  can  easily  be  seen  by 
comparison  that  the  diameter  of  the  circle  increases  with  the 
thickness  of  the  paper.  The  expansion  of  the  wetted  surface  is 
the  same  whether  the  paper  be  thick  or  thin,  provided  that  the 
material  of  each  and  degree  of  wetting  is  the  same.  The  thickness 
of  the  paper,  other  things  being  equal,  bears  a  direct  ratio  to  the 
diameter  of  the  circle.  The  greater  the  coefficient  of  expansion 
of  the  paper  the  smaller  the  circle  for  any  given  thickness. 

The  lecturer  has  done  a  lot  of  work  in  order  to  ascertain 
whether  the  curve  actually  found  agrees  with  the  calculated 
curve,  which  is  easily  arrived  at  when  the  expansion  of  the  paper 
is  known. 

These  do  not  agree  very  closely,  although  they  do  approxi¬ 
mately.  The  reason  of  this  is  that  some  of  the  moisture  soon 
finds  its  way  through  the  body  of  the  paper  and  expands  that  also. 
If  the  ratio  of  the  thickness  to  the  circle  can  be  established  by 
experiment,  the  curves  of  papers  of  known  thickness  may  be 
compared  and  their  coefficient  of  expansion  easily  calculated  by 
means  of  a  paper  coated  on  one  surface  only  with  a  material  which 
will  render  it  impervious  to  moisture  and  so  prevent  expansion  on 
the  unwetted  side.  I  hope  to  be  able  to  determine  the  coefficient 
of  expansion  of  a  paper  on  wetting  from  the  arc  of  the  circle 
produced  with  a  paper  of  known  thickness. 

When  paper  is  heated  on  one  surface  only,  provided  the  heat 
be  applied  evenly  and  rapidly,  the  curvature  is  the  same  as  when 
wetted,  only  in  the  opposite  direction. 

Paper  does  not  expand  equally  in  all  directions.  In  order  to 
fully  understand  this  it  is  necessary  to  have  some  knowledge  of 
the  conditions  of  its  manufacture.  The  writer  advanced  a  theory, 
which  is  based  upon  certain  observations  made  by  Professor 
Tyndall  and  the  geologist  Sorby,  in  regard  to  the  origin  of  slaty 
cleavage.  This  was  published  (Chemical  News,  September  21st, 
1894).  A  portion  of  this  I  give  in  order  that  we  may  understand 
the  effects  of  water  in  causing  expansion  and  curling  of  machine- 
made  papers. 

“  Slaty  cleavage  is  in  no  sense  due  to  the  stratification  of  the 
rock  during  its  formation,  as  the  planes  of  cleavage  stand  in 
most  cases  at  right  angles  to  the  bedding.  Geologists  are  satisfied 


67 


that  it  is  distinct  from  crystalline  cleavage.  Mr.  Sorby,  the 
geologist,  found  that  plates  of  mica  are  a  constituent  of  slate 
rock.  He  found  by  applying  pressure  to  a  mass  containing  scales 
of  oxide  of  iron  and  sand  that  the  scales  tended  to  set  themselves 
at  right  angles  to  the  pressure  exerted,  and  to  allow  of  cleavage 
in  the  direction  of  the  plates. 

“  In  the  process  of  manufacture  of  papdr  the  pulp  as  it  passes 
on  to  the  endless  wire  of  the  machine  consists  of  ultimate 
vegetable  fibres,  such  as  cotton  and  linen  and  wood,  suspended  in 
a  large  volume  of  water.  The  specific  gravity  of  these  fibres  is 
about  1.5.  It  must  be  remembered  that  they  differ  from  plates  of 
mica  in  that  they  present  no  plane  surfaces. 

“  As  the  mass  passes  on  to  the  wire  it  receives  a  lateral  shake 
which  tends  to  set  the  fibres  at  right  angles  to  the  force  exerted 
by  the  shake.  This  might  be  at  right  angles  to  the  surface  of  the 
liquid,  or  in  a  plane  parallel  to  it.  The  latter  direction  appears 
to  be  determined  partly  by  the  force  of  gravity,  which  first  of  all 
carries  the  fibres  through  the  medium  in  which  they  are  suspended, 
and  then  causes  them  to  press  one  on  the  other.  The  fibres  are 
retained  by  the  wire  gauze,  but  the  watery  medium  filters  through. 
Water  unable  to  filter  through  is  removed  by  (1)  suction  boxes, 
and  (2)  the  press  rolls.  The  water  is  then  removed  by  forces 
acting  at  right  angles  to  the  surface  of  the  web,  so  that  we  have 
two  sets  of  forces,  one  exerted  in  a  direction  at  right  angles  to 
that  in  which  the  web  is  travelling,  but  in  a  plane  parallel  to  the 
surface  of  the  web,  and  the  second  in  a  vertical  direction.  These 
two  forces  acting  together  cause  the  fibres  to  lie  in  the '  direction 
in  which  the  web  is  travelling.” 

The  articles  from  which  the  above  extract  is  taken  was 
written  with  a  view  of  establishing  the  theory  then  propounded 
by  the  lecturer,  that  the  formation  of  paper  in  the  web,  or  on 
the  band  mould,  is  brought  about  by  the  same  forces,  and  in  the 
same  manner  as  slaty  cleavage  in  slate  rock.  It  is  here  quoted  to 
explain  the  “  lay  ”  of  the  fibres  in  a  sheet  of  machine-made  paper. 

With  machine-made  papers  the  curvature  takes  place  more 
readily  in  one  direction,  and  this  fact  has  been  utilised  for  deter¬ 
mining  the  direction  the  paper  has  come  from  the  machine.  This 
method  is  described  by  Herzberg  in  bis  book  on  u  Paper-Testing,” 
as  follows  : — 

“  If  it  is  necessary  to  find  which  is  the  machine  direction, 
and  when,  owing  to  the  sheet  being  damaged,  the  direction 
cannot  be  distinguished  with  certainty,  a  circular  piece,  about  ten 
centimeters  (four  inches)  in  diameter  is  cut  out  of  the  sample 

c  2 


68 


and  allowed  to  float  some  seconds  on  water.  It  is  then  taken 
carefully,  by  the  aid  of  forceps,  and  laid  on  the  palm  of  the  hand 
(to  which  it  must  not  be  allowed  to  stick),  when  the  edges  will 
be  bent  up  until  they  finally  overlap.” 

The  dotted  line  running  through  all  three  is  the  direction  of 
the  web  of  paper  on  the  machine. 

Herzberg  says :  41  The  explanation  of  this  test  is  this.  The 
side  of  the  paper  in  contact  with  the  water  absorbs  moisture, 
causing  the  fibres  to  swell  and  bend  the  paper;  as  the  paper 
expands  more  in  the  “  cross  ”  than  in  the  “  machine  ”  direction 
the  edges  in  the  first-named  rise.” 

The  above  appears  to  me  to  be  only  a  partial  explanation  of 
the  paper’s  behaviour,  as  I  think  will  be  made  apparent  after  a 
more  careful  examination  of  the  disposition  of  the  fibres  in  a  sheet 
of  machine-made  paper. 

Mr.  Little,  in  his  book  on  “  The  Chemistry  of  Papermaking,” 
describes  a  more  simple  test  for  determining  the  direction  of  the 
web  in  a  sheet  of  machine-made  paper.  It  is  as  follows: — Two 
strips  are  cut  from  a  sheet,  each  one  inch  wide  by  four  inches 
long ;  one  piece  is  cut  across  the  sheet  and  the  other  in  the  length 
of  the  sheet.  They  are  held  together  between  the  finger  and 
thumb  at  the  lower  end,  and  allowed  to  hang  to  one  side.  If 
they  remain  together  the  underneath  one  is  cut  in  the  machine 
direction.  If  they  remain  apart  at  their  loose  ends,  the  upper 
one  has  been  cut  in  the  direction  of  the  machine  or  web. 

The  forces  which  act  on  a  web  of  paper  as  it  passes  over  the 
machine,  as  we  have  already  seen,  cause  the  fibres  to  lie  in  the 
direction  of  the  web,  giving  the  sheet  greater  rigidity  in  one 
direction.  We  know  that  a  blind  made  of  stout  cane  bound 
together  with  thread,  is  only  slightly  flexible  in  the  direction  of 
the  strips  of  cane,  but  rolls  up  with  great  ease  in  the  other 
direction.  Now,  a  sheet  of  paper  wetted  on  one  side  expands  on 
the  wetted  side,  and  the  paper  curls  in  the  direction  in  which 
there  is  the  least  resistance,  which  is  across  the  web. 

I  have  found  it  preferable  not  to  float  the  disc  of  paper  on 
water,  but  to  wet  it  by  passing  it  on  to  a  well  wetted  pad  by 
means  of  a  glass  plate  or  other  flat  surface.  There  is  no  danger 
of  getting  the  upper  side  wetted  by  this  method,  and  the  paper  is 
more  readily  removed. 

1  have  found  it  somewhat  difficult  to  obtain  the  inverse  effect 
by  rapidly  heating  a  disc  of  machine-made  paper  on  one  surface 
only.  It  is  probable  that  the  contraction,  after  the  air-dry  stage 
has  been  reached,  is  very  slight.  It  has  been  remarked  early  in 


69 


this  article,  that  when  a  sheet  of  paper  is  exposed  to  the  rays  of 
the  sun,  or  brought  close  to  a  fire,  that  the  paper  curls  so  that 
the  concave  surface  is  pointed  towards  the  source  of  the  rays  of 
heat.  If  this  is  not  performed  under  certain  conditions,  it 
sometimes  happens  that  the  paper  is  curled  in  the  opposite 
direction,  namely,  with  the  convex  surface  facing  the  source  of 
heat.  This  is  noticed  sometimes  when  a  sheet  of  paper  that  has 
for  some  time  been  exposed  to  a  somewhat  damp  atmosphere  is 
brought  suddenly  in  contact  with  a  hot  metallic  surface.  The 
paper  quickly  begins  to  curl  with  the  ends  uppermost.  This  is 
due,  in  my  opinion,  chiefly  to  the  fact  that  the  moisture  from  the 
heated  surface  which  is  in  contact  with  the  metal,  cannot  escape 
except  by  passage  through  the  thickness  of  paper  and  from  the 
upper  surface.  Immediately  the  paper  becomes  heated  throughout 
its  thickness  (which  takes  but  a  few  seconds),  moisture  begins  to 
escape,  leaving  the  upper  surface  dryer  than  the  under  surface, 
and  so  causing  the  paper  to  curl  with  its  convex  surface  facing 
the  source  of  heat. 

An  interesting  effect  is  got  by  bringing  a  paper  of  medium 
thickness,  but  somewhat  damper  than  air-dry,  over  a  Bunsen 
flame  or  over  an  ordinary  gas  burner.  The  hot  air  from  the 
flame  impinging  on  the  under  surface  of  the  paper,  rapidly  dries 
it,  whilst  the  upper  surface  still  remains  damp.  This  causes  the 
paper  to  curl  down  towards  the  flame.  If  the  paper  be  retained 
in  this  position  it  curls  back  to  its  former  shape,  in  consequence 
of  the  moisture  leaving  the  upper  surface  when  the  heat  has 
passed  right  through  the  paper. 

It  must  be  borne  in  mind  that  paper  acts  quite  differently  to 
fabrics  when  wetted.  When  stiffened  pieces  of  fabric  are 
brushed  over  their  surface  with  a  damp  sponge  or  floated  for  a 
moment  on  water,  they  commence  rapidly  to  curl,  but  instead 
of  the  wetted  side  curling  outwards,  as  with  paper,  it  frequently 
curls  inwards.  The  only  cases,  so  far  as  I  am  aware,  in  which 
the  wetted  surface  curls  outwards,  as  with  paper,  are  those  in 
which  some  material  is  used  to  dress  the  fabric  which  rapidly 
expands  when  wetted,  and  when  this  expansion  is  greater  than 
the  natural  contraction  of  the  fabric  itself,  the  material  curls 
with  its  wetted  side  inwards. 

The  materials  used  for  dressing  bookbinders’  cloth  and  such 
like  are  the  same  as  U3ed  for  sizing  paper,  such  as  gelatine,  glue, 
and  starch.  This  leads  me  to  suppose  that  the  sizing  materials 
used  in  paper  are  largely  responsible  for  its  behaviour  towards 
water. 


70 


In  the  case  of  paper,  the  curling  influence  of  the  sizing 
materials  cannot  very  readily  be  determined,  as  these  materials 
curl  in  the  same  direction  as  the  fibre  substance  of  the  paper 
itself.  With  cloth,  however,  the  two  tend  to  go  in  opposite 
directions,  and  a  lot  of  information  may  be  obtained  by  using  a 
stiffened  fabric  that  has  been  coated  with  some  sizing  agent 
on  one  surface  only.  If  a  piece  so  prepared  be  wetted  on  the 
fabric  side  it  curls  generally  with  the  wetted  side  inwards,  and 
if  coated  on  the  filmed  side  it  curls  generally  with  the  wetted  side 
outwards.  Sometimes  a  stiffened  fabric  when  wetted  on  the 
uncoated  side  remains  almost  flat  for  some  time.  This  is 
probably  due  to  the  contraction  of  wetted  fabric  being  so  feeble 
that  it  is  unable  to  bend  the  coating.  When  the  dampness 
has  penetrated  the  coating  is  expanded  and  the  material  begins 
to  curl. 

There  are  important  practical  issues,  as  well  as  theoretical, 
in  relation  to  this  question.  Thus  there  is  a  lot  to  be  learned 
about  the  behaviour  of  bookbinders'  materials  when  wetted  with 
glue  or  paste.  Bookbinders  are  obliged  to  know  something  about 
these  peculiarities.  When  a  paper  is  stuck  to  a  board  or  rigid 
surface  it  is  damp  and  consequently  somewhat  expanded,  so  that 
as  it  dries  it  draw's  right  over  the  surface  and  takes  out  all  the 
creases.  A  strong  paper  so  stuck  is  capable  of  exerting  enormous 
force  as  it  dries  or  contracts  by  the  slow  application  of  heat. 
I  have  known  a  paper  under  these  conditions  to  tear  up  a  piece  of 
stone.  This  is  merely  the  effect  of  contraction  or  attempted 
contraction  of  paper  due  to  the  drying  of  the  fibres. 

Gelatine  or  glue — a  common  constituent  of  both  fabrics  and 
paper — expands  readily  in  water,  and  if  it  be  of  good  quality,  on 
immersion  in  water  it  swells  up  sometimes  to  four  times  its 
former  volume.  Tub-sized  papers  contain  often  5  per  cent.,  and 
sometimes  as  much  as  8  per  cent,  of  gelatine.  The  gelatine 
fills  the  interstices  of  the  paper.  Starch  is  contained  in  most 
papers.  It  is  often  found  to  the  extent  of  2  per  cent.,  and 
sometimes  as  much  as  5  per  cent.  This  probably  expands  on 
wetting,  but  to  a  more  limited  extent  than  gelatine.  It  is 
difficult  to  say  how  far  these  substances  cause  paper  to  curl,  but 
it  is  probable  that  they  have  a  lot  to  do  with  it.  Any  substance 
that  is  not  easily  permeated  by  water  added  to  paper  to  render  it 
waterproof  may  increase  the  curling  properties  of  paper  by 
allowing  one  surface  to  get  damp  whilst  the  other  is  unaffected. 
Rosin  has  this  effect,  and  it  is  for  this  reason  that  Herzberg 
recommends  its  use  when  it  is  desired  to  test  a  machine-made 


71 


water-leaf  paper  by  the  disc  method  to  find  the  direction  of 
the  web. 

It  is  very  difficult  to  understand  why,  on  the  one  hand, 
paper  should  expand  on  being  wetted  and  a  fabric  should 
contract.  It  appears  that  the  greater  the  expansion  of  the 
ultimate  fibres  themselves  the  greater  the  contraction  of  the 
cloth  or  fabric  made  from  the  same.  This  may  be  exemplified  as 
follows : — When  cotton  is  treated  with  very  strong  alkali  a 
process  goes  on  known  as  mercerisation.  The  cotton  fibres  are 
swollen  up  and  largely  increased  in  size.  If  a  cotton  fabric 
be  treated  in  the  same  liquid  the  area  becomes  very  much 
lessened.  Mercer,  who  discovered  this,  found  a  contraction 
of  about  20  per  cent.  The  interstices,  however,  are  largely  filled 
up.  When  a  cotton  waterleaf  paper  is  treated  in  the  same  way, 
a  large  increase  in  thickness  is  often  noticed.  If  a  strong  solution 
of  soda  be  allowed  to  fall  on  a  piece  of  paper  a  blister  is  formed 
by  the  swelling  of  the  paper  at  this  point.  Physically,  the 
action  of  water  when  the  paper  or  fabric  is  wetted  may  be 
regarded  as  the  same  in  kind  as  a  strong  solution  of  caustic  soda, 
but  the  action  is  not  nearly  so  intense.  Water  is  not  merely 
taken  up  by  the  fibre  as  a  sponge  takes  up  water,  but  it 
probably  enters  into  chemical  union  with  the  cellulose.  There 
is  no  doubt  that  it  altogether  alters  the  physical  properties 
of  the  fibres.  It  is  to  this  change  in  physical  properties  that 
fibres  undergo  when  acted  on  by  water  that  we  owe  their 
peculiar  power  of  felting  into  sheets  of  paper. 

It  has  already  been  shown  that  the  fibres  of  a  machine-made 
paper  lie  for  the  most  part  in  the  direction  of  the  web.  It  can 
easily  be  imagined  that  such  a  paper  would  tear  much  more 
readily  in  the  direction  of  the  web  than  across  it. 

Machine-made  papers  are  often  25  per  cent,  stronger  in 
the  “  cross”  direction  than  in  the  “  machine  ”  direction.  With 
common  news  I  have  known  several  cases  where  the  difference 
is  far  greater.  The  “  cross  ”  direction  is  three  times  the  strength 
of  the  “machine”  direction.  Such  a  difference  is  almost 
incredible,  but  it  often  occurs  in  ordinary  practice.  There  are  1 
other  reasons,  however,  than  the  mere  fact  that  the  fibres  are 
mostly  in  one  direction.  These  other  reasons  I  hope  to  give  you 
later.  Paper  shrinks  very  readily  in  width  when  on  the  machine,, 
and  the  direction  of  the  fibres  probably  has  a  great  deal  to  do 
with  the  shrinkage.  The  paper  being  kept  “taut”  lengthwise 
would  prevent  its  shrinkage  in  that  direction,  and  cause  an. 
increased  shrinkage  in  the  “  cross  ”  direction.  When  paper  is. 


72 


wetted  after  making  it  tends  to  assume  its  old  shape,  namely, 
the  shape  it  had  in  the  wet  state  when  first  made.  It  would  be 
necessary  in  order  to  do  this  that  it  expands  more  in  the  “  cross  ” 
than  in  the  machine  direction. 

If  the  paper  wetted  happens  to  be  a  glazed  one,  the  glazed 
surface  is  removed  and  the  paper  assumes  both  the  surface  and 
thickness  it  had  before  glazing.  In  other  words,  immersion  in 
water  undoes  the  work  of  the  calender.  The  same  thing  takes  place 
only  in  a  milder  degree  in  damp  air.  One  of  the  causes,  perhaps 
the  chief  one,  for  paper  going  hack  in  surface  after  calendering 
is  the  dampness  in  the  air  causing  the  paper  to  become  damp. 

In  order  to  get  the  watermark  of  the  paper  right  in  the 
sheet,  it  is  often  necessary  to  stretch  the  paper,  either  in  the 
direction  of  its  length  or  its  width.  This  stretch  probably  gives 
the  paper  an  increased  power  of  curling  when  the  same  becomes 
damped  or  heated,  as  already  explained. 

The  question  of  paper  curling  is,  I  think,  an  important  one, 
and  should  be  studied  with  the  view  of  overcoming  it. 

In  the  case  of  a  fabric,  the  warp  and  the  weft  resemble  the 
strands  of  a  piece  of  twine  in  that  they  consist  of  twisted  or 
spun  fibres  or  filaments.  The  direction  of  a  fibre  in  a  piece  of 
cloth  or  twine  is  that  of  a  helix,  whereas  the  fibres  in  a  piece  of 
paper  lie,  for  the  most  part,  in  the  direction  of  its  length  and  in 
the  same  plane  as  the  surface.  The  difficulties  already 
mentioned  in  regard  to  the  lateral  expansion  of  machine-made 
paper,  which  cause  a  disc  of  the  same  to  curl  in  one  direction, 
are  experienced  in  a  much  less  degree  with  hand-made  paper.  As 
we  have  already  seen,  that  lateral  shake  of  the  machine,  together 
with  the  forces  exerted  by  the  suction  boxes,  press  rolls,  &c., 
results  in  the  fibres  lying  in  the  direction  of  the  web,  or  what  is 
known  as  the  “  machine”  direction.  In  the  process  of  the  manu¬ 
facture  of  paper  by  hand  the  mould  receives  a  shake,  first  in  one 
direction  and  then  in  another  at  right  angles  to  the  first.  The 
fibres  always  try  to  assert  themselves  in  one  direction  when 
shaken.  If,  then,  the  shake  be  exerted  equally  in  each  direction, 
the  fibres  would  have  no  tendency  to  lie  in  any  one  direction, 
and  we  should  expect  to  find  them  disposed  in  all  directions 
throughout  the  sheet. 

In  practice  this  is  very  hard  indeed  to  ensure.  When  the 
mould  is  lifted  from  the  vat  by  the  operator,  he  gives  it  a  few 
shakes — say,  from  side  to  side — as  he  is  standing.  This  would 
tend  to  make  the  fibres  point  in  one  direction.  Next  he  gives  a 
set  of  shakes  in  the  opposite  direction  to  the  first,  namely,  to 


73 


and  from  him.  This  tends  to  make  the  fibres  lie  in  a  direction 
at  right  angles  to  the  first  layer.  All  the  time  that  he  is 
shaking  the  water  is  finding  its  way  through  the  wire  and  the 
fibres  are  subsiding.  The  effect  of  the  two  sets  of  shakes  is  to 
dispose  the  fibres  in  layers,  the  fibres  of  each  layer  being  different 
in  direction  to  the  one  above  it.  This  is  a  great  improvement  on 
machine-made  paper,  but  is  by  no  means  perfect,  as  the  paper  is 
disposed  in  layers  instead  of  consisting  of  one  mass  of  fibres 
disposed  in  all  directions.  It  must  be  remembered  also  that 
it  is  almost  impossible  for  an  operator  to  so  adjust  the  shakes  as 
to  make  one  set  of  fibres  just  compensate  for  its  neighbour,  and 
so  produce  a  paper  of  equal  strength  in  all  directions.  I  think 
I  am  right  in  saying  that  even  the  best  hand-made  papers  are 
very  seldom  of  uniform  strength  in  all  directions.  All  the  same 
for  this,  hand-made  papers  are  sufficiently  uniform  in  strength  for 
all  practical  purposes,  and  if  we  could  only  discover  some  means  of 
attaining  as  uniform  a  result  on  the  Fourdrinier  machine,  provided 
it  did  not,  of  course,  add  to  the  cost  of  manufacture,  a  great 
step  in  advance  would  be  accomplished  in  machine-made  paper. 

The  other  set  of  forces  corresponding  with  the  suction  boxes, 
couch-rolls,  and  press-rolls  comes  into  play  with  hand-made 
papers  when  the  same  are  pressed  between  felts.  These  forces 
cause  the  fibres  to  lie  in  the  same  direction  as  the  surface  of  the 
paper,  and  prevent  them  from  lying  in  the  direction  of  its  section. 
If  it  were  not  for  this  fact,  the  expansion  of  paper  when  wetted 
would  probably  be  much  more  uniform. 

We  next  come  to  consider  the  qualifications  of  an  ideal 
paper.  One  important  qualification  should  he  that  the  fibres 
“  lay  ”  equally  in  all  directions.  In  a  hand-made  paper  this  may, 
to  a  certain  extent,  be  accomplished  in  the  aggregate,  but  when 
the  paper  is  examined  in  section  it  will  probably  be  found  that 
layers  exist  of  fibres  disposed  in  opposite  directions  ;  moreover, 
the  after-pressure  of  the  felts  causes  the  fibres  to  lie  in  the  same 
plane  as  the  surface  of  the  paper.  In  an  ideal  paper  the  fibres 
should  not  only  “lay”  in  every  horizontal  direction,  but  in  all 
directions  whether  horizontal  or  vertical. 

In  spite  of  the  fact  that  most  papers  expand  when  wetted, 
they  can,  in  a  measure,  be  so  prepared,  when  circumstances 
demand  it,  as  to  expand  or  contract  very  little  with  change  of 
moisture  in  the  air.  It  is  important  for  some  purposes  that 
paper  should  not  alter  more  than  yL  in.  or  ^  in.  on  a  length  of 
12  inches.  With  paper  used  for  taking  the  records  of  meteoro¬ 
logical  observations  this  is  a  question  of  some  moment.  With 


74 


other  papers  the  amount  of  expansion  is  not  so  material, 
provided  that  the  expansion  is  the  same  in  the  two  directions. 

It  is  quite  easy  to  represent  by  means  of  a  rough  sketch 
the  relative  positions  of  fibres  in  an  ideal  paper,  showing  just  how 
the  fibres  should  be  disposed  if  they  could  be  discriminated  by 
means  of  a  microscope  in  the  paper.  It  may  be  taken  generally 
that  cellulose  expands  when  wetted.  I  am  not  aware  that  any 
measurements  have  been  made  of  the  expansion  of  ultimate 
vegetable  fibres  when  wetted.  It  appears  that  the  ultimate  fibre, 
say  of  cotton,  expands  more  in  diameter  than  in  length. 

I  think  there  is  good  reason  to  believe,  also,  from  the 
behaviour  of  ultimate  fibre  towards  certain  reagents  under  the 
mici’oscope,  that  the  increase  is  chiefly  at  the  expense  of  the 
diameter  of  the  fibre.  From  this  we  would  infer  that  when  a 
machine-made  paper  is  thoroughly  wetted  the  percentage  increase 
is  least  in  the  “  machine  ”  direction,  most  in  the  direction  of  the 
•thickness  of  the  paper,  and  the  percentage  increase  across  the  web 
lies  somewhere  between  these  two  extremes.  The  expansion 
of  a  paper  is  so  intimately  connected  with  its  liability  to 
curling  that  the  latter  cannot  be  fully  understood  without  a 
full  knowledge  of  the  former. 

With  chromo-lithographic  work  it  is  important  that  the 
paper  should  not  expand  with  moisture,  as  the  colours  are  thrown 
out  of  register.  The  expansion  should  be  slight  and  as  far  as 
possible  equal  in  the  two  directions.  Moisture  has  a  marked 
and  beneficial  effect  upon  some  printing  papers.  Damping  has  a 
softening  effect,  as  already  explained ;  it  overcomes  a  harshness 
which  is  objectionable.  If  the  paper  has  been  over-dried  as  it 
leaves  the  machine,  damping  before  printing  is  often  necessary. 
Damping  before  calendering  is  also  needed.  Paper  if  too  dry 
will  not  take  kindly  to  the  calendering  treatment.  On  the  other 
hand,  too  much  damping  must  be  avoided.  The  happy  medium 
must  be  aimed  at,  as  well  as  absolutely  uniform  distribution,  such 
as  can  now  be  accomplished  by  modern  systems  of  damping  done 
by  means  of  a  fine  spray. 

In  conclusion,  I  will  briefly  refer  to  the  destructive  influence 
of  water.  In  damp  atmospheres  papers  are  far  more  liable  to 
putrefaction  and  decay  than  in  dry  atmospheres,  more  particularly 
when  the  air  is  both  hot  and  damp.  Under  such  conditions 
bacterial  and  putrefying  organisms  flourish.  The  Indian  climate 
is  destructive  to  papers,  even  hard-sized  papers,  not  because  of 
the  heat  alone,  but  because  of  the  moisture  in  conjunction  with 
the  beat. 


LECTURE  VI. 


CHEMICAL  RESIDUES  IN  PAPER. 

Metallic  salts — Purity  of  ash — Lime  salts  clue  to  bleach — Influence  of 
acidity — Discharge  of  lines — Presence  of  iron — Reasons  for — Amount  in 
raw  materials — Chemistry  of  rusting — Prevention  of  rusting — Effects  of 
iron  in  water  on  paper — Elimination  of  iron  during  manufacture — Test  for 
iron — Iron  in  chemicals — In  finished  papers — Iron  and  other  metallic 

particles. 


In  these  lectures  I  am  adopting  what  I  believe  to  be  a 
novel  expedient.  In  most  of  them  I  am  adopting  a  thesis  as  it 
were.  I  give  you  a  test  or  subject,  or  perhaps  it  would  be  better 
to  say  an  aspect  of  papermaking,  for  your  consideration.  The 
endeavour  is  made  to  elaborate  on  whatever  aspect  is  chosen,  and 
to  garner  a  few  at  least  of  the  facts  bearing  on  the  question  at 
issue.  Some  of  the  questions  I  venture  to  think  are  novel,  at  any 
rate  as  forming  the  subject  of  a  lecture.  They  tread  on  more  or 
less  debatable  grounds,  but  this  we  cannot  help,  because  if  we 
avoid  debatable  grounds  we  shall  make  very  little  progress.  If 
we  are  to  treat  only  of  well-tried  and  well-tested  questions  that 
have  been  written  upon  times  without  number,  we  might  as  well, 
to  use  a  slang  expression,  shut  up  shop  as  far  as  this  course  of 
lectures  is  concerned.  I  should  then  merely  draw  them  to  a  close 
by  referring  you  to  current  literature  on  the  subject.  But  I  am 
engaged  to  come  here  and  put  before  you,  to  the  best  of  my 
ability,  fresh  subject-matter,  or.  at  any  rate,  fresh  aspects  of 
papermaking  for  your  consideration.  The  extent  to  which  you 
may  profit  by  it  will  depend  very  largely  as  to  whether  it  does 
what  Carlyle  declared  to  be  that  which  is  the  greatest  help  that 
can  be  conferred  upon  a  man.  It  should  help  you  to  help  your¬ 
selves.  If  by  these  lectures  you  are  better  able  to  acquire  further 
knowledge  for  yourselves  some  lasting  benefit  may  accrue,  but  if 
you  go  away  and  think  no  more  about  them,  whether  they  have  any 


76 


V* 


intrinsic  merit  in  themselves  or  no,  I  can  hold  out  no  hopes  that 
you  will  be  benefited. 

I  admit  that  these  lectures  may  be  over  the  heads  of  some  of 
those  who  attend,  but  this  is  inevitable  in  a  mixed  class.  It  is 
for  this  reason  that  I  have  decided  during  the  actual  delivery  of 
the  lectures  to  give  you  more  elementary  details  than  the  text 
contains,  and  in  many  places  not  to  stick  to  the  text  at  all,  in 
fact,  often  to  branch  off  into  other  subjects  which  may  appear 
more  palatable  and  suitable  to  the  individual  members.  By  this 
system  you  have  really  a  twofold  advantage,  for  you  have  the 
advantage  of  hearing  me  speak  upon  more  elementary  details,  and 
joining  in  a  discussion  afterwards,  and  you  have  the  opportunity 
of  reading  through  copies  of  the  proofs,  and  discussing  them 
afterwards,  should  you  desire  to  do  so. 

The  subject  of  this  lecture  is  perhaps  a  difficult  one,  but  is 
important  and  at  the  same  time  fascinating,  both  to  the  chemist 
and  to  the  papermaker.  It  more  particularly  interests  makers  of 
high-class  papers.  My  attempt  is  here  not  so  much  to  give  a  lot  of 
solid  information  as  to  indicate  by  what  little  information  is  herein 
given  a  method  by  which  further  may  be  acquired. 

It  is  important,  at  any  rate  to  the  maker  of  photographic 
paper,  that  his  paper  should  contain  little  or  no  metallic  salts. 
In  order  to  avoid  the  introduction  of  metallic  salts  he  must  have 
a  ready  means  of  testing  his  products  during  their  various  stages 
of  preparation. 

There  is  the  question  of  ash  in  pure  paper.  If  the  ash  is  to 
be  kept  down,  perhaps  for  the  purpose  of  complying  with  some 
specification,  the  processes  that  give  rise  to  the  ash  should  be 
traced,  and  when  the  causes  of  the  introduction  or  removal  of  ash 
are  known,  the  exact  quantity,  even  in  pure  papers,  which  are 
supposed  to  contain  none,  can  be  more  or  less  controlled.  I  have 
known  a  paper  to  contain  10  percent,  of  ash,  not  through  the  clay 
or  other  mineral  being  added,  but  through  the  peculiar  power  that 
the  said  fibre  possessed  in  condensing  the  lime  salts  from  the 
bleach  solution  added  to  bleach  it.  This  of  course  is  an 
extreme  case. 

Then  we  have  the  question  of  the  exact  condition  of  the 
paper  as  regards  so-called  acidity  or  alkalinity,  with  which  I  hope 
to  deal  in  a  future  lecture.  This,  again,  is  a  question  of 
chemical  residues. 

Furthermore,  we  have  the  question  which  has  caused  so  much 
trouble  at  different  times  of  papers  affecting  printers’  inks  or 
printers’  inks  affecting  papers,  so  as  to  give  rise  to  a  pungent 


77 


smell.  This  is  a  difficult  and  intricate  one,  and  one  only  upon 
which  some  chemist  skilled  in  the  detection  of  very  minute 
chemical  residues  could  form  any  opinion.  While  admitting  that 
paper  may  be  prepared  so  as  to  overcome  this  nuisance,  it  must 
be  admitted  that  the  blame,  if  any,  rests  as  much  with  the 
inkmaker,  or  the  printer  who  will  insist  on  using  a  common-made 
ink,  as  with  the  papermaker,  because  a  remedy  is  as  often  effected 
by  changing  the  ink  as  by  changing  the  paper. 

The  same  question  has  also  been  raised  in  connection  with 
certain  well-known  makes  of  writing  inks,  as  being  unnecessarily 
penetrating  with  tub-sized  papers,  even  with  the  best  makes.  It 
would  seem  that  in  this  last-mentioned  case  the  inkmaker  should 
do  what  he  can  to  meet  the  difficulties  of  the  papermaker; 
whether  he  has  done  so  I  have  no  means  of  judging. 

Then  we  have  the  qualities  of  minute  chemical  residues  in 
papers  in  their  effect  upon  analine  inks.  The  faint  lines  ruled 
upon  some  foolscap  paper  appear  to  fade  away  fairly  rapidly  on 
some  common  papers.  I  should  have  liked  to  suggest  that  it  is 
confined  to  the  common  paper.  It  appears  to  take  place  more 
readily  when  the  papers  are  allowed  to  get  even  the  least  bit 
damp.  The  question  again  arises — Is  it  the  fault  of  the  papers,  or 
is  it  due  to  the  fugitiveness  of  the  colour  used?  It  may  be  either 
or  both.  We  certainly  do  not  want  to  find  after  a  few  years  that 
our  press  copies  of  type-written  letters  have  faded  away,  so  that 
they  are  no  longer  legible.  Under  certain  conditions  this 
undoubtedly  does  take  place,  both  with  the  copy  and  the  original, 
whereas,  under  other  conditions,  as  far  as  we  at  present  know, 
they  remain  permanent,  or  nearly  so.  Sometimes  the  press  copies 
or  originals  are  inclined  to  bleed  or  become  blurred,  and  can  only 
be  read  with  great  difficulty.  The  Italian  Government  have  taken 
a  wise  precaution  in  prohibiting  the  engrossing  of  legal  documents 
by  means  of  the  typewriter.  In  the  United  States  it  is  a  very 
common  custom  to  draft  legal  documents  by  means  of  the  type¬ 
writer.  It  will  be  interesting  to  see  what  attitude  they  will  take 
now  that  they  meditate  the  establishment  of  a  State  laboratory 
to  go  into  such  matters. 

We  will  now' trace  the  presence  of  iron  as  a  metallic  impurity 
through  the  different  stages  of  papermaking. 

^Doubtless  many  of  us  are  not  aware  that  the  salts  of  iron 
are  in  some  way,  at  present  unexplained,  intimately  connected 


*  This  article  is  largely  abstracted  from  an  article  on  the  presence  of  iron  in 
paper,  which  I  originally  contributed  to  the  Paper-Maker. 


78 


with  the  life  and  growth  of  the  animal  and  vegetable  kingdom 
around  us.  All  the  members  of  the  plant  world  that  elaborate  for 
themselves  their  food  from  the  inorganic  constituents  of  the  soil, 
and  from  the  invisible  nourishing  gases  of  the  atmosphere,  are 
possessed  of  a  green  substance  known  as  “chlorophyll,”  which 
enables  them  to  convert  these  inorganic  lifeless  bodies  into  a 
part  of  their  own  living  structure.  This  wonderful  substance 
“  chlorophyll,”  which  seems  to  form  a  chain  between  the  living 
and  the  dead,  invariably  contains  iron  salts.  Without  iron  salts 
plants  would  be  divested  of  their  green  colour.  A  very  simple 
experiment  illustrates  this.  If  we  take  a  few  grains  of  Indian 
corn  and  place  them  in  water  which  contains  all  the  necessary 
ingredients  for  their  growth,  with  the  simple  exception  of  iron, 
the  Indian  corn  will  sprout  and  grow  to  a  certain  degree,  but  it 
will  be  found  devoid  of  colour.  If  the  surface  of  the  leaf  be 
touched  with  the  solution  of  a  salt  of  iron,  or  if  the  solution  be 
added  to  the  water,  the  leaves  will  develop  the  green  colour  due 
to  the  presence  of  chlorophyll,  which  will  enable  the  plants  to 
continue  their  growth.  With  retted  flax  and  fabrics  that  are 
more  or  less  cleansed  of  chlorophyll,  that  remaining  is  easily 
recognised  by  the  brilliant  blue  venation  when  the  chemical 
reagent  for  iron  is  applied. 

The  blood  of  animals  contains  a  red  substance  known  as 
haemoglobin,  which  gives  to  the  blood  its  characteristic  colour. 
This  substance  invariably  contains  iron,  which  amounts  to  0.42 
per  cent,  on  the  weight  of  the  haemoglobin.  Here,  again,  iron  has 
a  most  important  function  to  perform. 

The  bearing  that  the  above  facts  have  on  the  subject  of  this 
lecture  are  soon  made  manifest. 

All  substances  of  animal  and  vegetable  origin  are  found,  as 
might  well  be  inferred  from  the  above,  to  contain  iron.  Paper 
consists  of  substances  that  are  mostly  of  vegetable  origin  :  thus 
cotton,  linen,  wood,  straw,  esparto,  and  other  vegetable  fibres,  as 
well  as  such  substances  as  starch  and  rosin.  It  also  contains 
substances  of  animal  origin,  the  chief  of  which  is  gelatine. 

The  chemicals  used  also  are  found  to  contain  some  iron  salts, 
so  that  we  may  safely  say  that  all  materials  used  in  the  manufac¬ 
ture  of  paper  contain  iron. 

When  an  organic  substance  is  burnt  the  iron  remains  in  the 
ash,  and  can  be  recognised  by  dissolving  in  a  little  nitric  acid, 
adding  water,  filtering,  and  adding  a  few  drops  of  potassium 
ferrocyanide  solution,  when  a  blue  coloration  is  produced  due  to 
the  formation  of  Prussian  blue.  The  depth  of  this  coloration  is  a 


79 


measure  of  the  amount  of  iron  present.  The  amount  of  iron  can 
be  exactly  determined  by  comparison  with  a  solution  containing  a 
known  quantity  of  iron. 

The  following  determinations  will  be  found  useful  for  refer¬ 
ence.  All  raw  materials  are  subject  to  a  considerable  variation 
in  the  amount  of  iron  they  contain,  but  these  figures  are  fairly 
representative,  being  the  result  of  a  large  number  of  analyses. 

Parts  of  iron  per 
hundred  thousand. 


Cotton  wool  .  .  .  .  .  .  6.0 

New  pieces  .  .  .  .  .  .  1.0 

Unbleached  cotton  .  .  .  .  14.0 

New  canvas  .  .  .  .  .  .  18.0 

Bag  dust  .  .  .  .  .  .  .  .  175.0 

Dirty  rags  .  .  .  .  .  .  65.0 

Clean  rags  .  .  .  .  .  .  25.0 

Eosin  size  .  .  .  .  .  .  .45 

Crystal  alum,  pure  recrystallised  .043 
Sulphate  of  alumina  .  .  .  .  .35 

Mechanical  wood  (aspen)  .  .  10.0 

Aspen  wood  .  .  .  .  .  .  5.0 

Bleached  sulphite  wood  pulp  .  .  8.0 

Bleached  pulp  from  aspen  wood.  .  12.0 


Thus  we  see  that  pure  cellulose,  as  cotton  wool,  new  pieces, 
or  any  other  form,  contains  little  iron. 

With  flax  the  extent  of  the  retting  and  after-treatment 
would  largely  determine  the  amount  of  iron  as  a  residue.  It 
follows  then  that  with  flax  or  linen,  the  more  the  fibres  are 
cleansed  of  iron  cellulose  the  less  the  iron.  W  ith  raw  materials, 
such  as  skins,  the  more  thorough  the  treatment  for  the  removal 
of  blood  and  hair  the  less  the  iron  as  a  residue. 

But  rags  contain  a  very  considerable  quantity  on  account  of 
the  dirt  and  foreign  matter  containing  iron  with  which  they  are 
contaminated.  That  this  dirt  contains  a  large  amount  of  iron  is 
shown  by  the  very  large  quantity  found  in  rag  dust.  We  must 
not  look  on  rag  dust  as  consisting  of  dirt  only,  as  it  contains  on 
an  average  about  50  per  cent,  of  cellulose.  The  iron  which  rags 
contain  due  to  the  dirt  is  not  so  difficult  of  removal  as  that 
natural  to  the  fibre.  On  evaporating  down  some  of  the  spent 
liquors  from  boiling  rags,  I  found  considerable  quantities  of  iron, 
sufficient  to  account  for  the  loss  of  iron  that. the  rags  sustain  by 
this  treatment. 


80 


Iron  mordanted  rags  contain  a  very  large  amount  of  iron, 
which  is  very  difficult  to  remove.  When  these  I’ags  are  boiled  in 
caustic  soda,  the  colouring  matter  in  combination  with  the  iron 
is  mostly  removed,  but  the  iron  remains  firmly  embedded  in  the 
fibre,  and,  probably,  then  exists  as  magnetic  oxide  of  iron.  When 
these  rags  are  treated  with  bleach  solution,  especially  when  the 
bleach  is  used  in  warm  solution,  the  rags  are  considerably 
tendered — sometimes  they  are  quite  rotten.  The  explanation  of 
this  tendering  action  is  as  follows.  Bleaching  powder  solution, 
when  used  with  ordinary  care,  merely  acts  on  the  organic  colouring 
matter  of  the  rags,  oxidising  it  into  colourless  soluble  products. 
The  solution  has  little  or  no  action  on  the  cellulose.  When, 
however,  the  rags  contain  oxide  of  iron  the  action  is  different. 
The  oxide  is  reduced  to  ferrous  oxide,  giving  up  its  oxygen  to  the 
cellulose,  converting  it  into  oxycellulose,  which  results  in  the 
disintegration  of  the  fibre.  The  ferrous  oxide  is  converted  back 
into  ferric  oxide  by  the  oxygen  supplied  to  it  by  the  bleaching 
powder.  It  then  undergoes  a  similar  cycle  of  changes,  being 
alternately  oxidised  and  reduced,  and  so  merely  acts  as  a  bearer  of 
oxygen  to  the  fibre.  The  importance  of  the  removal  of  iron 
before  the  bleaching  operation  cannot  be  over-estimated.  This  is 
generally  done  by  souring  with  muriatic  acid,  whereby  the 
insoluble  ferric  oxide  is  converted  into  soluble  ferric  chloride, 
which  is  removed  by  washing.  The  removal  of  iron  is  often 
effected  by  souring  the  rags  immediately  after  boiling.  INo  doubt 
a  considerable  quantity  is  removed  by  boiling  and  washing,  but 
what  is  left  is  very  hard  indeed  to  remove,  even  on  prolonged 
souring.  By  far  the  best  order  is  to  give  the  rags  a  good  souring 
before  boiling,  when  the  iron  is  much  more  readily  removed. 
The  material  will  not  only  be  much  less  acted  on  by  the  bleach 
solution,  but  will  be  a  much  better  colour. 

A  large  amount  of  the  iron  found  in  papers  is  derived  from 
the  iron  tanks,  boilers,  beaters,  washers,  &c.,  with  which  the 
material  comes  in  contact.  As  the  metallic  iron  has  first  to  be 
converted  into  iron  rust  before  it  can  be  imbedded  in,  or  discolour 
the  pulp,  we  must  next  consider,  What  is  rust?  How  is  it 
formed?  and  how  may  it  be  prevented  ? 

Iron  rust  is  generally  supposed  to  be  ferric  oxide  (Fe203), 
and  to  contain  no  other  oxides  of  iron.  Recent  researches,  how¬ 
ever,  have  revealed  the  fact  that  rust  also  contains  a  large  amount 
of  magnetic  oxide  (Fe304b  Research  has  also  revealed  the  fact 
that  iron  cannot  rust  in  air  deprived  of  carbonic  acid  gas,  neither 
can  it  rust  in  air  containing  no  moisture.  It  seems  also  most 


81 


probable  that  iron  cannot  rust  even  in  pure  oxygen.  The 
explanation  of  this  is  plain.  Iron  shares  with  all  other  metals 
the  property  of  condensing  on  its  surface  a  film  of  moisture. 
Carbonic  acid  gas  is  very  soluble  in  water,  therefore  the  film  of 
metallic  iron  contains  a  considerable  quantity  of  carbonic  acid, 
derived  from  the  atmosphere.  Ordinaiy  air  contains  4  parts  of 
carbonic  acid  (C02)  per  10,000.  Carbonic  acid  in  contact  with 
iron  becomes  reduced  to  carbonic  oxide  (CO),  at  the  same  time 
oxidising  the  iron. 

Carbonic  oxide  on  meeting  with  the  oxygen  of  the  atmo¬ 
sphere  is  oxidised  again  to  carbonic  acid,  and  so  the  carbonic  acid 
merely  acts  as  a  bearer  of  oxygen  from  the  atmosphere,  and  the 
film  of  water  is  the  medium  through  which  it  is  conveyed. 

The  action  is  really  more  complicated  than  this,  for  a  small 
quantity  of  ammonia  is  formed,  due  to  the  combination  of  the 
hydrogen  of  the  water  with  the  nitrogen  of  the  atmosphere. 

We  often  notice  that  a  bright  surface  of  iron  is  some  time 
before  it  begins  to  rust,  but  that  when  once  the  action  is  started 
it  goes  on  with  ever-increasing  rapidity.  The  reason  of  this  is 
that  in  course  of  time  we  have  a  layer  of  magnetic  oxide,  and  a 
layer  of  ferric  oxide.  These  two  layers  set  up  a  galvanic  action 
which  results  in  the  more  rapid  oxidation  of  the  metal. 

Now  we  know  the  exact  conditions  which  attend  the  formation 
of  rust  we  are  able  to  find  a  remedy.  Caustic  soda  solution  has  a 
great  affinity  for  carbonic  acid,  combining  with  it  to  form  sodium 
carbonate.  If  we  have  any  iron  tanks  or  boilers  lying  empty, 
and  we  wish  to  prevent  the  formation  of  rust,  we  must  fill  them 
with  water  containing  a  little  caustic  soda,  which  seizes  hold  of 
the  carbonic  acid  gas  before  it  has  a  chance  of  reaching  the  iron. 

We  now  see  why  rusting  is  worse  at  or  near  the  surface  of 
the  water  in  an  iron  tank. 

It  follows  from  the  above  that  there  need  be  no  fear  of 
rusting  of  boilers  that  are  constantly  used  for  alkali  boils. 

Water  used  for  washing  is  likely  to  contain  iron  derived 
from  the  rusting  of  the  tanks  in  which  it  is  stored,  and  this  is 
often  found  to  be  the  case.  I  found  that  water  of  the  following- 
composition — 

15  grains  of  carbonate  of  lime  per  gallon, 

6  grains  of  sulphate  of  lime  per  gallon, 

5  parts  of  iron  per  ten  million  of  water, 
on  being  left  in  contact  with  1  per  cent,  of  its  weight  of  iron  for 
three  days,  contained  at  the  end  of  that  time  50  parts  per  10 


82 


million.  The  metallic  iron  was  at  the  bottom  of  the  vessel 
containing  the  water. 

The  danger  of  using  water  contaminated  with  even  traces  of 
iron  is  that  cellulose  has  a  great  affinity  for  iron  salts,  which  it 
removes  even  from  very  dilute  solutions.  The  following  experi¬ 
ment  exemplifies  this  : — 

Some  pure  cellulose  was  placed  in  twelve  times  its  weight  of 
water,  the  water  contained  10  parts  of  iron  per  10,000.  On  taking 
out  and  thoroughly  washing,  the  cellulose  was  found  to  contain 
one-third  of  the  iron. 

A  piece  of  paper  consisting  of  cotton  and  linen  was  similarly 
treated,  and  was  found  to  have  abstracted  half  the  iron  from  this 
very  dilute  solution. 

Before  treatment  the  paper  contained  15  parts  of  iron  per 
100,000,  after  treatment  it  contained  70  parts  per  100,000.  A 
large  number  of  other  trials  might  be  cited,  but  they  all  show  that 
cellulose  has  the  power  of  attracting  iron  even  in  very  dilute 
solutions. 

Unfortunately  iron  has  the  power  of  imparting  a  brownish 
tint  to  cellulose  when  the  former  is  present  even  in  very  minute 
quantities. 

We  would  expect  to  find  that  the  iron  natural  to  the  fibre  is 
uniformly  distributed  throughout  the  whole  mass  of  the  fibre. 
With  cotton,  which  belongs  to  the  seed  hairs,  this  is  the  case,  but 
with  linen  this  is  not  so.  Let  us  take  a  piece  of  linen  fabric  and 
immerse  it  in  water  containing  1  per  cent,  of  potassium  ferro- 
cyanide  and  a  few  drops  of  nitric  acid ;  in  three  hours  we  shall 
find  that  the  fibres  have  developed  a  blue  colour ;  some  of  the 
filaments  will  be  found  to  be  much  bluer  than  others.  The  flax 
fibre  has  to  undergo  a  process  of  retting,  whereby  the  green  pulpy 
matter  containing  the  chlorophyll  is  removed  from  the  fibre.  If 
this  process  is  not  complete,  some  of  the  iron  contained  in  the 
chlorophyll  may  become  part  and  parcel  of  the  fibre,  even  after 
the  chlorophyll  has  been  destroyed.  This  is  bound  to  result  in 
an  irregular  distribution  of  the  iron  in  the  different  fibres. 

Some  lignified  fibres  contain  a  large  amount  of  iron,  which, 
however,  is  readily  removed,  as  it  is  in  combination  with  sub¬ 
stances  that  are  removed  by  the  chemical  treatment.  The 
following  is  a  typical  instance  : — 

A  sample  of  Sunn  hemp  fibre  contained  250  parts  of  iron 
per  100,000. 

The  paper  made  from  the  same  contained  only  6  parts  per 

100,000. 


83 


We  next  come  to  consider  the  several  ingredients  added  to 
the  fibre  in  the  course  of  manufacture. 

Alum  and  sulphate  of  alumiua.  For  a  long  time  these  two 
compounds  entered  into  keen  competition.  Sulphate  of  alumina 
has  for  many  years  been  cheaper  pro  rata  than  alum,  but  it  was 
not  used  for  high-class  papers,  as  it  contained  both  free  acid  and 
a  considerable  quantity  of  iron.  Many  attempts  were  made  to 
remove  the  last  traces  of  iron,  with  the  result,  now,  that  sulphate 
of  alumina  can  be  obtained  nearly  as  free  from  iron  as  crystal 
alum,  if  we  except,  perhaps,  Turkey  red  alum,  which  is  purified 
from  iron  by  repeated  crystallisation.  This  is  of  very  great 
importance,  for  the  greater  part  of  the  alum  finds  its  way  into 
the  finished  paper. 

The  iron  present  in  starch  is  so  small  that  it  may  be  neglected. 

The  question  arises,  does  the  paper  derive  any  iron  from  the 
various  iron  fittings  of  the  paper  machine  ?  I  endeavoured  to 
solve  this  question  by  taking  pieces  of  paper  at  different  stages  of 
manufacture,  and  have  not  yet  been  able  to  detect  any  increase  in 
the  amount  of  iron  as  the  paper  passes  over  the  machine. 

Thus,  in  one  instance,  I  found  a  piece  torn  off  immediately 
after  passing  through  second  press  rolls  contained  7  parts  of  iron 
per  100,000. 

The  same  after  it  had  passed  over  iron  drying  cylinder,  7 
parts  of  iron  per  100,000. 

The  best  method  of  determining  whether  tub-sizing  increases 
the  amount  of  iron  is  to  take  a  piece  of  the  water-leaf  and  a 
piece  of  the  paper,  after  tub-sizing,  and  determine  the  amount  of 
iron  in  each.  The  difference  will  represent  the  amount  of  iron 
due  to  gelatine  and  alum  in  the  trough. 

If  we  know  the  amount  of  iron  in  the  alum  and  the  propor¬ 
tion  of  alum  we  are  using,  we  can  soon  calculate  what  is  due  to 
the  gelatine.  The  amount  of  iron  in  the  gelatine  varies  con¬ 
siderably  with  its  quality  and  source. 

The  iron  in  finished  paper  can  be  shown  in  a  rough-and-ready 
way  by  cutting  the  pieces  under  examination  into  strips  and 
immersing  them  in  1  per  cent,  solution  of  potassium  ferrocyanide, 
together  with  a  few  drops  of  nitric  acid,  in  a  photograph  dish. 
The  dish  should  be  covered  over  with  a  glass  plate  and  the  samples 
left  in  for  three  hours,  at  the  end  of  which  time  they  will  all  have 
developed  a  blue  colour,  in  depth  equal  to  the  amount  of  iron 
present.  The  samples  should  be  washed  and  dried.  The  blue 
colour  thus  produced  is  very  permanent,  and  the  samples  can  be 
kept  for  years  without  fading.  This  method  thus  affords  us  a 


84 


means  of  determining  whether  the  papers  made  from  time  to 
time  undergo  any  change  in  the  amount  of  iron  they  contain. 
The  very  compound  here  produced  is  used  in  the  manufacture  of 
paper  for  giving  it  a  blue  tint.  It  is  well  known  that  papers 
coloured  with  Prussian  blue  fade  very  rapidly  under  certain 
conditions.  The  Prussian  blue  is  added  to  the  pulp  as  a 
precipitate,  whereas  the  trace  of  Prussian  blue  formed  by  adding 
potassium  ferrocyanide  to  a  paper  containing  a  trace  of  iron  is 
formed  in  situ.  A  great  deal  of  iron,  undoubtedly,  has 
thoroughly  penetrated  into  the  cell  wall  of  the  fibre  and  has 
become  fixed  and  largely  converted  into  ferric  oxide.  The 
Prussian  blue  is  then  formed  within  the  cell  wall,  and  so  is 
imprisoned,  thus  rendering  it  much  less  sensitive  to  light. 

For  an  accurate  determination,  however,  this  method  cannot 
be  made  use  of.  If  the  paper  under  examination  is  not  white, 
if,  for  instance,  it  has  a  yellow  tint,  the  blue  developed  is  partially 
neutralised  by  the  yellow,  and  the  paper  appears  to  contain  less 
iron.  The  iron  must  then  be  estimated  by  taking  a  weighed 
quantity  of  the  paper,  burning  it,  and  determining  the  iron  either 
by  the  colorimetric  or  gravimetric  method. 

The  following  are  determinations  made  in  these  methods  : — 


Iron-  in  News — 

Parts  of  Iron 

8  different  samples  analysed — 

per  100,000. 

Greatest  amount 

60.0 

Least  amount  ... 

4.0 

Mean 

39.6 

Periodicals  and  Journals — 

13  different  samples  analysed — 

Greatest  amount 

30.0 

Least  amount  ... 

3.0 

Mean 

16.7 

Book  Papers — 

4  different  samples  analysed — 

Greatest  amount 

25.0 

Least  amount 

8.0 

Mean 

12.5 

Mean  of  all  analyses  of  all  paper 

tested 

22.9 

The  mean  is  not  the  figure  midway  between  the  greatest  and 
the  least,  but  represents  the  total  iron  in  all  the  analyses  divided 
by  the  number  of  analyses. 


85 


The  samples  were  taken  from  among  the  leading  papers. 
These  results  show  that  the  better-class  papers  contain  much  less 
iron  than  the  lower  class,  and  this  is  what  we  might  well  expect. 

Paper  frequently  contains  metallic  particles,  and  many  of 
these  consist  of  iron.  Some  of  these  particles  would  escape 
detection,  as  they  are  too  small  to  be  distinguished.  When, 
however,  the  paper  is  immersed  in  the  acidulated  potassium 
ferrocyanide  solution,  the  particles  of  metallic  iron  are  rendered 
evident  by  the  production  of  intensely  blue  spots. 

Often,  however,  metallic  particles  are  due  to  the  presence 
of  brass  derived  from  the  beater  knives,  and  often  from  the 
buttons  in  the  rags,  in  which  case  the  paper  on  immersion  in  the 
same  reagent  will  develop  chocolate-coloured  spots,  showing  the 
presence  of  copper. 

It  is  important  to  have  a  ready  means  of  determining  the 
presence  of  metallic  particles  as  well  as  metallic  salts.  Iron 
particles  sometimes  found  in  papers  are  objectionable,  as  they 
may  give  rise  to  iron  mould,  especially  if  the  paper  gets  at  all 
damp.  This  mould  may  eat  away  the  paper  as  it  does  a  fabric. 
Brass  is  less  objectionable  in  this  respect,  although  it  should  not 
be  allowed  to  enter  into  better-class  papers.  Zinc  is  sometimes 
found  on  the  rims  of  buttons.  I  published  an  easy  method  for 
the  detection  of  brass  or  copper  particles  in  the  Chemical 
News.  It  merely  consisted  in  placing  a  bead  of  water,  in  which 
nitrate  of  silver  was  dissolved,  over  the  suspected  particle,  and 
covering  same  with  a  watch  glass,  and  leaving  it  in  a  dark  place ; 
if  brass  or  copper  were  present  arborescent  crystals  of  metallic 
silver  soon  grew  on  the  spot  where  the  brass  particle  was,  and 
copper  went  into  solution  ;  with  iron  no  change  took  place. 


LECTURE  VII. 


*  CHEMICAL  RESIDUES  IN  PAPERS  ( continued ). 
Definition  of  paper — Contamination  of  paper  from  raw  materials — Lime 
boiling — Removal  by  subsequent  washing — Impure  caustic — Fixation  of 
lime  from  water  by  fibres — Effects  of  different  materials  added  to  the 
chest — Mode  of  testing  papers — Indicators — Chemical  condition  of  paper 
—  Soluble  constituents  —  Insoluble  constituents  —  Effects  of  metallic 
residues  at  high  temperatures — Behaviour  of  iodide  paper — Acidity  and 
alkalinity  of  different  papers. 


Paper  has  been  defined  by  some  writer  as  being  an  aqueous 
deposit  of  any  vegetable  fibre.  Perhaps  a  more  adequate  and 
brief  definition  could  hardly  be  given.  It  appears,  however,  to 
require  a  certain  limitation  in  order  that  the  definition  may  not 
include  certain  articles  which  could  not  be  classed  as  paper.  In 
order  to  do  this,  I  should  define  paper  as  the  aqueous  deposit  of 
any  vegetable  fibre  in  the  form  of  a  web  or  sheet.  To  leave  out 
the  word  vegetable  appears  to  be  a  mistake.  Although  woollen 
and  silk  rags  may  be  deposited,  and  also  asbestos  fibres,  they  can 
hardly  be  classed  as  forming  the  basis  of  paper. 

In  addition  to  that  which  forms  the  fibrous  basis  or  network, 
namely,  the  vegetable  fibre  deposited  from  its  suspension  in  water, 
we  have  other  materials  which  almost  invariably  form  part  of  the 
paper,  among  which  are  gelatine,  starch,  rosin-size,  alum,  soap, 
and  minerals. 

The  raw  material  during  its  preparatory  treatment  undergoes 
a  course  of  chemical  treatment  to  free  it  from  that  which  is 
useless. 

The  resulting  material,  which  consists  of  some  form  of 
cellulose,  acts  as  a  magnet  to  the  various  chemicals  used  in  its 
preparation.  These  are  more  or  less  retained  by  the  paper,  and 
play  an  important  part  in  its  after-life  and  history. 

*  The  Author  discussed  this  subject  at  some  length  in  the  columns  of  the  Paper-Maker 
as  an  outcome  of  his  paper  on  “The  Acid  Action  of  Drawing  Papers,”  which  was  read 
before  the  Chemical  Society  as  a  criticism  of  certain  conclusions  arrived  at  by  Professor 
Hartley,  FE.S,,  in  regard  to  Whatman’s  Drawing  Papers. 


87 


In  addition  to  the  above  substances,  which  steal  into  the 
finished  paper  by  being  hidden  and  occluded  by  the  cell-wall  of 
the  paper,  should  be  mentioned  those  substances  which  are  added 
to  the  pulp,  or  the  unfinished  paper,  to  give  it  weight,  or  some 
new  property.  The  latter  often  exist  in  larger  quantities  than 
the  former,  but  they  are  generally  associated  with  the  fibre  in  a 
different  manner,  and  appear  to  have  a  greater  external  influence, 
such  as  upon  substances  used  to  coat  the  paper.  Those  substances 
which  are  embodied  in  the  cell-wall  appear  to  exert  a  more  im¬ 
portant  influence  upon  the  fibre  itself. 

W  e  will  attempt  at  first  to  briefly  trace  the  former  substances. 
Most  raw  materials  are  subjected  to  an  alkaline  treatment  for  the 
removal  of  (a)  in  the  case  of  such  materials  as  cotton,  linen,  rags, 
&c.,  foreign  matter,  with  which  the  fibre  is  contaminated;  (h)  in 
the  cases  of  such  substances  as  wood,  straw,  and  esparto,  for  the 
removal  of  substances  that  are  not  foreign  to  the  raw  material, 
but  are  in  combination  with  it,  and  form  part  of  the  original  fibre 
substance.  The  cellulose  residuum,  after  the  removal  of  these 
substances,  has  a  much  greater  power  of  absorbing  soluble  salts 
and  bases  than  those  classed  under  (a).  Jute  bagging  and  un¬ 
bleached  linen  rags  belong  to  both  classes,  as  they  both  contain 
a  large  amount  of  contaminating  matter,  and  also  substances  in 
combination  with  their  respective  cellulose,  but  capable  of  partial 
removal  by  the  alkaline  treatment. 

The  alkaline  treatment  above  referred  to  is  generally  either 
that  of  boiling  with  lime  or  caustic  soda.  Lime  is  seldom  used, 
except  when  class  (a)  is  under  treatment.  The  lime  enters  into 
combination  with  the  foreign  matter  to  form  an  insoluble  soap, 
and  is  used  in  revolving  boilers.  The  compounds  formed  are 
insoluble  soaps  which,  being  friable,  are  dislodged  from  the  fibre 
by  the  mechanical  agitation  due  to  the  motion  of  the  boiler. 
Provided  that  the  after-processes  of  washing  are  thorough,  very 
little  lime  is  left  in  contact  with  the  material  ;  its  removal  is 
always  associated  with  a  corresponding  loss  of  those  foreign 
substances  with  which  it  has  entered  into  combination. 

The  caustic  soda  forms  soluble  salts,  which  enter  into  solution 
in  the  boiling  liquor  at  the  time  of  their  formation.  It,  however, 
contains  impurities,  unless  the  highest  grades  are  used,  which 
militate  against  its  beneficial  action  ;  among  them  may  be  men¬ 
tioned  iron  and  alumina.  The  former  is  insoluble  in  caustic  soda 
solution  at  the  strength  at  which  it  is  used,  and  can  only  be 
associated  with  the  fibrous  material  as  ferric  oxide  or  magnetic 
oxide. 


88 


It  may  or  may  not  be  readily  removed  by  the  subsequent 
mechanical  treatment  during  washing.  The  latter  substance,, 
alumina,  may  be  contained  in  the  boiling  liquor  as  sodium 
aluminate.  If  the  caustic  liquor  is  not  very  strong,  and  the 
water  used  for  its  mixture  and  dilution,  prior  to  coming  in  con¬ 
tact  with  the  fibre  contains  a  considerable  quantity  of  lime  salts, 
the  lime  is  rendered  insoluble,  and  forms  a  flocculent  precipitate 
of  the  hydrate,  which,  to  a  large  extent,  becomes  intermingled  with 
the  fibre.  If  the  alumina  is  allowed  to  gain  access  to  the  fibre 
as  sodium  alumina,  it  is  absorbed  and  condensed  by  the  former 
during  the  treatment.  It  is  highly  probable  that  sodium  aluminate 
dissociates  readily  in  situ ,  and  produces  alumina  within  the  cell- 
wall.  This  being  the  case,  no  amount  of  chemical  treatment  or 
washing  will  remove  it,  and  therefore  it  finds  its  way  into  the 
finished  paper  as  an  insoluble  base.  Some  papers,  even  after 
thorough  washing,  are  found  to  contain  large  amounts  of  bases, 
which  are,  for  the  most  part,  insoluble  fixed  bases  incapable  of 
removal  by  treatment  in  water  alone,  and  not  by  any  means  easy 
to  remove  by  treatment  with  acids. 

Low  grade  caustic  sodas  contain  impurities  which  militate 
against  the  chemical  action  of  the  free  caustic.  This  has  been 
referred  to  in  a  previous  lecture.  It  should  be  pointed  out, 
however,  that  when,  say,  60  per  cent,  caustic  is  dissolved  up  in  a 
copper,  and  diluted  to,  say,  16°  Twaddle  with  hard  water,  and 
pumped  to  a  store  tank,  as  is  often  the  case  in  practice,  much  of 
the  impurity  is  removed  as  scum  or  sediment,  so  that  the  clear 
liquor  as  drawn  from  the  store  tank  is  considerably  purified. 
Where  low  grade  caustic  is  used  this  modus  operandi  should 
certainly  be  resorted  to,  as  it  adds  considerably  to  the  purity  of 
the  alkali,  and  as  a  consequence  to  the  economy  of  boiling. 

When  the  unbleached  but  boiled  material  is  subjected  to  the 
action  of  bleaching  powder,  the  lime  salts  are  readily  condensed 
in  some  cases.  Notice  that  lime  salts  are  condensed  by  cellulose 
residues,  such  as  in  the  case  of  bleaching  with  calcium  hypo¬ 
chlorite,  whereas  the  lime  salts  are  not  condensed  in  a  lime  boil, 
but  enter  instead  into  combination  with  the  encrusting  matter,  for 
subsequent  removal  in  an  insoluble  form  by  washing.  The  lime 
absorbed  by  the  fibre,  if  in  contact  with  the  atmosphere,  is  con¬ 
verted  into  carbonate  of  lime,  which  is  nearly  insoluble.  I  have 
found  by  comparing  the  ash  before  and  after  bleaching,  a  very 
large  increase,  due  to  the  formation  of  carbonate  of  lime  with 
some  fibres  containing  low  yields  of  cellulose  With  materials 
belonging  to  class  (a),  little  or  no  increase  is  noticed,  but  in  class 


89 


(6),  where  the  residuum  often  contains  considerable  quantities  of 
oxycellulose,  the  gain  is  very  marked.  I  have  found  where  the 
bleach  consumed  in  one  case  amounted  to  about  30  per  cent, 
on  the  raw  fibre,  a  gain  of  per  cent,  in  the  ash  after  bleaching. 
With  the  purest  form  of  cotton  and  linen  rags  the  ash  is  found 
to  be  considerably  above  the  normal  of  raw  cotton.  The  power 
that  cellulose  has  of  retaining  soluble  salts  is  shown  when  stuff 
containing  a  considerable  excess  of  bleaching  powder  is  copiously 
washed  in  the  beater  or  breaker.  If  the  stuff,  and  also  the  solution 
that  it  contains,  be  frequently  tested  with  a  solution  containing 
soluble  starch  and  potassium  iodide.  At  a  point  where  the  water 
no  louger  gives  the  reaction,  the  stuff  will  still  be  found  to  yield 
the  blue  colour,  and  this,  after  the  washing  has  been  continued 
■for  a  considerable  time,  and  even  after  the  stuff  has  had  ample 
opportunity  of  assimilating  with  the  water.  If  the  washing  be 
stopped  for  some  time,  the  water  after  a  bit  is  found  to  contain 
•some  of  the  lime  salts.  It  happens  sometimes  that  the  washing 
is  too  rapidly  done  to  remove  the  whole  of  the  bleach,  in  which 
-case  it  is  retained  by  the  fibre.  It  is  not  long  before  the  stuff 
fails  to  give  the  blue  coloration  with  starch  and  potassium  iodide, 
due  to  the  fact  that  the  whole  of  the  free  chloride  present  has 
expended  itself. 

The  lime  salts  are  readily  fixed  in  the  fibre  by  the  bicarbonate 
of  lime  present  in  the  water  used  for  washing.  When  stuff 
containing  bleaching  powder,  no  matter  whether  the  free  chloride 
has  been  expended  or  not,  comes  in  contact  with  hard  water  con¬ 
taining  bicarbonate  of  lime,' the  free  lime  contained  in  the  cell- 
wall  of  the  fibre  is  converted  into  carbonate  of  lime  in  situ  by 
abstracting  carbonic  acid  from  the  water.  The  formation  of 
calcium  carbonate  in  situ  is  attended  by  the  formation  of  a  corre¬ 
sponding  quantity  of  calcium  carbonate  as  a  precipitate  in  the 
solution,  provided  there  be  no  free  carbonic  acid  in  the  water. 
Thus : — 

In  fibre.  In  water.  In  fibre.  In  water. 

CaO  +  Ca0(C02)2  =  CaC03  +  CaC03 

With  regard  to  the  bleaching  powder  itself  (Ca(C10)2),  the 
free  carbonic  acid,  and  probably  that  combined  to  form  calcium 
bicarbonate,  combines  with  the  calcium  to  form  the  carbonate,  and 
liberates  hypochlorous  acid.  Thus  : — 

Ca(C10)2  +  C02  +  H20  =  CaC03  +  2HC10. 

It  is  doubtful  to  what  extent  the  bicarbonate  of  lime  will 
yield  up  carbonic  acid  to  bring  about  this  change,  but  it  appears 
to  do  it,  to  a  large  extent,  with  some  waters. 


90 


The  explanation  of  the  assimilation  of  lime  salts  by  pulp 
whilst  bleaching  and  washing  may  be  summarised  as  follows : — The 
cellulose  absorbs  the  so-called  calcium  hypochlorite  from  its  solu¬ 
tion.  On  contact  with  hard  water  whilst  washing,  these  salts, 
before  their  removal  can  be  effected,  are  converted  into  insoluble 
calcium  carbonate  by  the  carbonic  acid  in  the  water.  That  which 
passes  away  is  often  found  to  be,  for  the  most  part,  hypochlorous  acid. 
This  action  is  also  assisted  by  the  carbonic  acid  contained  in  the 
air,  especially  when  the  material  is  agitated  during  the  treatment. 

If  the  bleach  in  the  beater  is  neutralised  with  an  antichlor,  it 
generally  adds  to  the  alkalinity  of  the  pulp.  Thus,  for  instance, 
when  sodium  sulphite  is  used — the  commercial  salt  itself  being  an 
alkaline  substance — the  alkalinity  is  increased.  To  reduce  the 
alkalinity  sodium  bisulphite  may  be  usel.  This  salt  oxidises  to 
sodium  sulphate  and  sulphuric  acid,  thus  : — 

2Na2S03S02  -f-  302  =  2Na2S04  -f-  2H2SOJ 
The  sulphuric  acid  so  formed  combines  with  some  of  the 
bases  present. 

When  rosin  size  is  used  the  resulting  compounds  are  theo¬ 
retically  neutral ;  but  it  seldom  happens  that  the  rosin  soap  and 
alum  are  used  in  equivalent  quantities.  According  to  the  equa¬ 
tion,  sodium  aluminate  should  be  formed.  The  latter  substance 
is  hardly  likely  to  be  formed,  as  the  hard  water  present  would 
bring  about  the  precipitation  of  alumina.  The  chemical  changes 
which  take  place  in  the  chest  are  exceedingly  complicated,  and 
vary  enormously  according  to  conditions. 

The  treatment  of  paper  stock  from  the  beginning  is  almost 
entirely  basic,  and  the  only  substance  likely  to  overcome  this 
basicity  is  the  alum  or  sulphate  of  alumina. 

I  will  take  an  individual  case  in  detail,  in  order  to  see  how 
far  the  basic  and  acid  substances  are  balanced. 

The  following  case  is  one  in  which  bisulphite  of  soda  was 
used  as  an  antichlor,  and  the  bleaching  done  in  the  beater.  The 
chest  contained  32  cwts.  of  dry  stuff. 

The  alum  was  added  as  a  20  per  cent,  solution  of  sulphate  of 
alumina,  which  was  added  to  the  stuff  as  follows  : — 

To  the  chest  .  .  .  .  .  .  45  gallons. 

To  the  machine  .  .  .  .  22  ,, 

To  the  gelatine  .  .  .  .  20  „ 

The  sulphate  of  alumina  was  used  up  in  the  following  ways 
in  neutralising  the  basic  substances  : — 

(1 )  Used  up  in  neutralising  hardness  of  water.  Water  Con¬ 
tained  17  grains  of  carbonate  of  lime  per  gallon.  The  stuff  in  the 


91 


chest  contained  4  per  cent,  of  fibre  and  96  per  cent,  water.  Tor 

32  x  100 

32  cwts.  of  fibre  we  should  then  have  - -4 - =  800  cwts., 


4 


17 


sav  90,000  lbs.  of  water.  Which  would  contain  ...... 

J  i  u,ouo 


of  90,000 


=  153,000  grains  of  carbonate  of  lime. 

Now,  114  parts  of  sulphate  of  alumina  are  required  for  each 

„  ni  .  ,  ,  .  153,000  x  114 

100  parts  of  lime.  Therefore,  we  should  require  - — 


=  174,000  grains  of  sulphate  of  alumina,  or  25  lbs.  of  sulphate 
of  alumina. 

(2)  Sulphate  of  alumina  to  neutralise  rosin  size.  Seven 
gallons  of  rosin  size  =  70  lbs.  at  10  per  cent.,  sodium  carbonate  = 
7  lbs.  of  carbonate,  which  =  8  lbs.  of  sulphate  of  alumina. 

Alum  in  chest  and  in  machine  added,  equal  together  57 
gallons  at  20  per  cent.  ;=  154  lbs.  of  sulphate  of  alumina. 

Nos.  (1)  and  (2)  above  together  consumed  33  lbs.  The 
amount  of  alum  we  should  expect  to  find  in  excess  would  be 
154-  33  =  121  lbs.  free  alum.  Therefore,  back-water  might  con¬ 
tain  121  in  90,000  =  .134  per  cent,  sulphate  alumina,  equal  to 


.134  X  98 
114 


.115  per  cent,  sulphuric  acid. 


The  paper  after  passing  through  press  rolls  was  found  to 

consist  of —  cvt  ,  ,  n, 

27  per  cent,  dry  fibre, 

73  per  cent,  water. 

The  wet  paper  was  found  ta  contain  alum  equal  to  0.26  per  cent, 
of  sulphuric  acid  on  the  dry  weight  of  fibre,  or  equal  to  .07  per 
cent,  on  the  water  contained  therein. 

It  is  probable  that  the  back-water  contained  less  alum  than 
the  above  figures,  as  cellulose  has  a  considerable  affinity  for  it, 
which  it  abstracts  from  the  back-water. 

By  calculation  we  find  the  figure  should  be  .115  per  cent., 
by  estimation  the  figure  is  found  to  be  .070  per  cent,  in  solution. 

The  difference  is  undoubtedly  due  to  not  making  allowances 
for  the  bases  in  the- pulp  before  it  entered  the  chest. 

We  next  pass  on  to  the  sulphate  of  alumina  added  to  the 
animal  size. 

20.0  gallons  at  20  per  cent.  =  40  lbs.  sulphate  alumina. 

40  x  98  „  ,  ,  . 

— — -  =  34  lbs.  sulphuric  acid. 


36  cwts.  of  sized  paper  =  4,032  lbs. 

4,032  lbs.=  34  lbs.  =  .8  per  cent,  on  the  weight  of  the  paper. 


92 


The  quantity  of  sulphate  of  alumina  added  to  the  size  can  be 
fairly  well  determined  by  taking  the  acidity  of  the  paper  before 
and  after  sizing.  It  must  be  borne  in  mind  that  the  alum  added 
to  the  animal  size  when  tub-sizing  is  resorted  to  all  enters  the 
paper,  whereas  that  added  to  the  chest  or  to  stuff  before  it  passes 
into  the  machine  is  diluted  with  the  water  in  which  the  fibres  are 
suspended,  and  its  retention  is  due  to  two  causes,  (1)  the  con¬ 
densing  power  that  cellulose  has  upon  alum  in  solution,  (2)  the 
moisture  contained  in  the  stuff  after  it  passes  the  second  press. 
In  the  case  of  the  above-cited  fibre,  we  find  that  the  water  was 
exhausted  by  .0269  per  cent.,  due  to  this  cause. 


This  would  add  to  the  acidity  of  the  paper 


.026  x  100 
27 


=  say  .1  per  cent,  acidity. 

With  regard  to  the  latter  cause,  provided  that  the  dilution  in 
the  chest  and  the  amount  of  water  contained  in  the  paper  after 
passing  the  second  press  be  known,  and  providing  no  wTater  is 
added  to  the  back-water  other  than  that  derived  from  the 
chest,  we  can  readily  calculate  the  amount  of  alum  retained,  and 
the  acidity  of  the  paper  due  to  this  cause. 

Supposing  we  have  in  the  chest  1  part  of  dry  fibre  to  25  of 
water,  as  above,  and  that  the  paper  also  contains  27  per  cent,  dry 
fibre  and  73  per  cent,  water;  after  the  second  press,  taking  the 
amount  of  alum  we  find  in  excess  in  the  chest,  101  lbs.  to 
19,600  lbs.  of  dry  fibre,  the  calculation  is  simply  as  follows:  — 

101  x  100x  100x100  ,  ,  ,  . 

— ^ — ,  n  onr, — 5= —  =.13  per  cent,  sulphate  of  alumina 

2oxl9,600x2/  r  1 

retained  by  paper  due  to  cause  (2). 

This  would  add  to  the  acidity  of  the  paper  to  the  extent  of 
.13x98 

— j-p; —  =  .11  per  cent,  in  terms  of  H2S04 

In  this  particular  case,  then,  by  far  the  greater  part  of  the 
acidity  of  the  paper  is  due  to  the  sulphate  of  alumina  added  tO' 
the  gelatine  for  tub-sizing,  although  this  only  formed  a  minor  part 
of  the  total  quantity  of  the  sulphate  of  alumina  used  altogether. 

The  following  is  a  summary  of  another  trial.  45  gallons  of 
20  per  cent,  of  sulphate  of  alumina  used  in  all : — 


Gallons. 

7  gallons  of  rosin  soap  consumed  .  6.88 

30  of  ordinary  hard  soap  consumed .  4.55 

7,168  gallons  of  hard  w^ater  consumed  .  .  .  .  20.45 

Balance  of  sulphate  of  alumina  .  13.12 


45.00 


93 


The  balance  is  partly  made  up  in  neutralising  the  bases  in  the 
pulp,  but  there  was  a  sufficient  amount  of  sulphate  of  alumina 
remaining  to  give  the  water-leaf  an  acid  reaction. 

Expressed  in  percentage  or  total  sulphate  of  alumina  used,  the 
consumption  is  as  follows  : — 

45.5  per  cent,  consumed  by  hard  water. 

15.3  ,,  „  ,,  I’osin  soap. 

10.1  „  ,,  ,,  hard  soap. 

29.1  ,,  ,,  ,,  bases  and  free. 

lOO'O  per  cent. 

The  unconsumed  sulphate  in  this  case  can  hardly  be  said  to  be 
wasted,  since  it  is  necessary  to  have  an  excess  to  ensure  complete 
precipitation  of  the  rosin,  and  a  rosin-sized  paper  should  always  be 
finished  slightly  acid  to  get  the  maximum  sizing  effect. 

Most  papermakers  would  be  surprised  to  hear  that  it  is  a 
matter  of  the  most  careful  adjustment  to  ensure  that  a  paper 
does  not  give  either  an  acid  or  an  alkaline  reaction.  With  paper 
that  is  used  for  a  great  many  purposes  it  is  a  matter  of 
indifference  whether  it  be  neutral  or  not,  but  with  some  paper 
a  little  care  in  this  respect  would  add  largely  to  its  value 
and  utility.  I  desire  merely  in  this  article  to  draw  attention  to 
this  matter,  and  to  show  as  far  as  possible  what  influence  the 
various  processes  to  which  the  raw  materials  are  subjected  and 
the  various  ingredients  used  in  the  course  of  manufacture  have 
upon  the  finished  product.  I  shall  attempt  also  to  give  some 
ready  means  for  the  examination  of  papers,  and  to  show  their 
behaviour  with  certain  indicators. 

Some  word  is  wanting  which  should  express  the  relationship 
of  a  paper  to  indicators,  such  as  litmus  and  methyl  orange — in 
short,  that  will  express  the  three  conditions  at  once  —  (1)  acidity, 
(2)  neutrality,  (3)  alkalinity.  It  might  be  called  chemical 
condition,  but  even  this  would  by  no  means  properly  define  the 
condition  wanted. 

There  is  the  strongest  objection  to  the  use  of  the  three  terms 
separately. 

If  we  find  that  a  certain  paper,  when  placing  on  a  drop  of 
weak  neutral  litmus,  turns  the  same  red,  are  we  right  in  saying 
that  the  paper  is  acid  because  acids  turn  litmus  red  ?  We 
immerse  the  same  paper  in  a  carefully  neutralised  solution  of 
Congo  red,  and  we  find  that  the  latter  will  go  the  same  colour 
that  it  would  if  an  alkali  was  added  to  it.  It  would  appear, 
then,  that  the  paper  was  alkaline. 


94 


We  try  the  same  with  methyl  orange,  and  this  also  indicates 
that  the  paper  is  alkaline.  Shall  we  call  the  paper  acid  or 
alkaline  ?  This  is  a  question  that  has  never  been  closely  studied. 
The  truth  is  that  acidity  or  alkalinity  is  only  a  matter  of  degree, 
as  heat  and  cold.  One  acid  is  stronger  than  another  and  is 
capable  of  replacing  it.  Also  one  alkali  or  base  is  stronger  than 
another.  It  may  be  said  that  the  stronger  acid  is  more  acid  than 
the  weaker,  also  that  the  stronger  base  is  more  alkaline  than 
the  weaker  base.  In  paper  we  have  certain  substances  always 
present,  which  consist  of  a  mixture  of  an  acid  and  a  base.  The 
same  substance  may  play  the  part  of  an  acid  or  a  base,  according 
as  the  substance  with  which  it  is  in  combination  is  more  acid  or 
basic  thau  itself.  Alumina  is  dissolved  by  soda  to  form  sodium 
aluminate,  when  it  acts  the  part  of  an  acid  substance.  If 
sulphuric  acid  is  added  to  this,  which  is  a  much  more  powerful  acid 
substance  than  alumina,  the  alumina  is  first  of  all  turned  out  by 
the  sulphuric  acid,  and  if  further  acid  be  added  it  turns  over  and 
becomes  the  base,  and  enters  into  combination  with  the  sulphuric 
acid  to  form  sulphate  of  alumina.  There  is  a  substance  known 
as  normal  alumina  sulphate.  When  these  two  substances  are 
compared  the  former  is  strongly  alkaline  to  the  latter,  or  the  latter 
acid  is  compared  with  the  former.  The  former  substance  is 
neutral  to  litmus  and  the  latter  to  congo  red.  Cross  and  Bevan 
found  that  the  neutral  point  with  methyl  orange  is  reached  when 
there  is  present  two  molecules  of  alumina  to  five  of  sulphuric  acid. 
With  congo  red  the  ratio  is  two  of  the  former  to  six  of  the  latter. 
With  a  paper  like  the  one  described,  if  alumina  and  sulphates  be 
present  (to  which  there  is  seldom  an  exception),  the  difference 
in  the  action  of  the  three  indicators  is  easily  explained.  And  by 
the  use  of  these  three  indicators  on  the  same  paper,  a  very  fair 
idea  is  obtained  as  to  what  I  am  forced  to  call,  for  want  of  a 
better  name,  “  the  chemical  condition  of  the  paper.”  The  paper 
being  alkaline  to  congo  red  shows  that  no  free  acid  is  present, 
the  paper  being  alkaline  to  methyl  orange  shows  that  there  must 
be  less  sulphuric  acid  in  combination  with  alumina  than  is 
expressed  by  the  ratio  2A12035S03.  The  fact  that  the  paper 
is  acid  to  litmus  points  to  the  probability  of  the  paper  containing 
a  low  sulphate  of  alumina,  although,  if  the  whole  of  the  alumina 
were  free,  or  even  some  of  it  in  combination  with  soda,  the  paper 
might  still  give  an  acid  reaction  with  litmus.  Our  ultimate  object 
in  thoroughly  understanding  the  behaviour  of  paper  in  regard  to 
various  indicators  is  to  throw  light  upon  the  action  of  the  paper 
in  regard  to  different  colours  and  inks.  It  must  be  borne  in  mind, 


95 


also,  that  a  knowledge  of  the  constitution  of  the  chemicals  in  the 
paper  will  be  of  help  to  us  in  ascertaining  whether  any  chemical 
change  is  likely  to  take  place  in  the  paper  itself  which  may 
result  in  the  paper  becoming  discoloured  and  rotten  when  kept 
for  a  great  length  of  time. 

When  congo  red  is  added  to  a  solution  of  alum  or  sulphate 
of  alumina  it  does  not  give  the  acid  reaction  unless  there  be  free 
acid  present.  The  same  holds  good  with  a  paper.  If  a  drop 
of  congo  red  be  placed  on  a  paper  and  it  turns  blue,  the  paper 
contains  free  acid ;  if  it  is  alkaline  to  methyl  orange  but  acid  to 
litmus  it  probably  contains  a  basic  sulphate  of  alumina ;  if  it  is 
basic  to  litmus,  which  is  often  the  case,  but  is  found  to  contain 
both  sulphate  and  alumina,  there  is  no  basic  sulphate  of  alumina 
present.  Alumina  may  be  present  in  the  free  state,  and  the 
sulphuric  acid  in  combination  with  lime  salts  as  sulphate.  When 
a  soluble  base  is  added  to  sulphate  of  alumina,  such  as  caustic  soda, 
the  neutral  point  with  litmus  is  reached,  just  when  the  whole  of 
the  sulphuric  acid  is  combined  with  soda  and  the  alumina 
precipitated.  Thus  : — 

Al23S04+6Na0H  =  3Na2S04  +  Al203+3H20. 

If  soda  be  added  in  excess  some  of  the  alumina  is  dissolved  to  form 
sodium  aluminate. 

Substituting,  say,  lime  as  a  base  for  caustic  or  carbonate 
of  soda,  we  get  the  whole  of  the  alumina  precipitated  until  we 
come  to  the  neutral  point  as  before,  but  an  excess  of  lime  is 
incapable  of  dissolving,  and- therefore  combining  with  the  alumina. 
We  then  get  a  paper  containing  free  bases,  that  is,  basic  to  litmus. 

The  most  ready  means  of  testing  paper  is  to  get  the  three 
indicators,  litmus,  methyl  orange,  and  congo  red,  and  prepare 
perfectly  neutral  and  very  dilute  solutions  of  each  with  recently 
boiled  and  rapidly  cooled  distilled  water.  A  bottle  of  each  of 
these  is  kept  from  contact  with  the  atmosphere.  A  stirring- 
rod  is  dipped,  say,  into  the  methyl  orange,  and  a  small  bead  from 
this  allowed  to  fall  upon  the  paper  to  be  examined.  At  equal 
intervals  drops  of  the  same  indicator  are  placed  side  by  side  so 
as  to  form  a  row  of  drops.  The  time  that  each  drop  has  been  in 
contact  with  the  paper  is  known,  and  its  rate  of  change  can  be 
noted  by  comparison  with  its  neighbour.  The  rate  at  which  the 
change  takes  place  can  be  taken  as  a  fair  indication  of  its 
chemical  condition.  To  guard  against  any  disturbances  due  to 
impurities  in  the  atmosphere,  the  strips  of  paper  should  be  covered 
with  watch  glasses. 


96 


A  better  way,  perhaps,  but  one  requiring  more  time,  is 
to  take  equal  weights  of  the  papers  under  examination  and  place 
them,  after  tearing  up,  into  equal  volumes  of  a  dilute  solution 
of  the  indicator.  This  is  best  done  in  ordinary  thin  tumblers, 
and  a  piece  of  glass  placed  over  each  to  prevent  contamination 
with  the  atmosphere.  After  allowing  to  soak  for  three  hours, 
the  fragments  of  paper  are  pushed  out  of  the  liquid,  and  the 
change  of  colour  of  the  solution  noted  against  an  equal  volume 
of  the  standard  solution  under  similar  conditions. 

The  two  above-mentioned  methods  are  only  qualitative,  and 
may  mislead  us  without  other  tests.  Only  those  substances, 
whether  acid  or  alkaline,  that  are  soluble  in  water  affect  the 
indicator,  so  that  we  only  get  an  idea  of  the  soluble  constituents. 

The  following  is  a  ready  method  of  determining  the  amount 
of  basicity  or  acidity  of  the  soluble  constituents.  Four  grammes 
of  the  paper  are  placed  in  a  beaker  and  digested  with  boiling 
distilled  water.  This  is  kept  in  an  air  bath  to  digest  at  about 
140°  Fahr.  for  three  hours.  The  hot  water  is  run  off,  and  the 
paper  twice  digested  with  hot  distilled  water.  Care  should  be 
taken  that  water  is  free  from  carbonic  acid.  To  the  aqueous 
extract  is  added  a  drop  of  neutral  litmus,  and  the  titration  is  per¬ 
formed  with  decinormal  sulphuric  acid,  if  the  extract  be  basic, 
and  if  acid,  with  decinormal  sodium  carbonate.  In  the  latter  case 
the  solution  must  be  boiled  to  expel  the  carbonic  acid,  and  if  by 
any  chance  too  much  of  the  sodium  carbonate  has  been  added, 

N 

the  solution  must  be  titrated  back  with  H.2S04.  The  writer, 

after  careful  trials,  abandoned  the  other  two  indicators,  methyl 
orange  and  phenol-phthlein,  as  the  presence  of  substances  such 
as  gelatine  seemed  to  mask  their  true  end  reaction. 

It  is  advisable  always  to  express  the  chemical  condition  of 
the  paper,  whether  it  be  acid  or  basic,  in  terms  of  sulphuric  acid, 
in  order  that  the  results  with  both  kinds  of  paper  may  be  capable 
of  comparisons. 

It  is  most  important  to  determine  the  chemical  condition 
of  the  paper  as  to  its  insoluble  constituents.  This  is  not  done 
with  the  same  amount  of  accuracy  as  the  soluble.  It  can  be  got 
at  by  determining  the  total  constituents  and  the  soluble  consti¬ 
tuents,  and  taking  the  difference  as  being  the  insoluble. 

Supposing  the  paper,  upon  superficial  examination,  gives  an 
alkaline  reaction  with  litmus,  and  that  the  amount  of  alkalinity 
of  the  constituents  is  determined  with  litmus,  a  fresh  quantity  of 
paper  is  taken  and  digested  with  hot  distilled  water  containing 


97 


three  times  the  quantity  of  acid  required  for  the  soluble  con¬ 
stituents.  It  is  twice  exhausted  with  distilled  water  as  before. 
To  the  extract  is  added  litmus ;  it  is  then  titrated  back  to  the 
neutral  tint  with  sodium  carbonate.  The  difference  between  the 
two  titrations  gives  us  the  alkalinity  of  the  total  bases.  The  risk 
that  we  run  here  is  of  some  of  the  acid  being  condensed  by  the 
cellulose,  and  also  the  cellulose  and  starch  being  acted  upon  by 
the  acid.  The  after-washings  with  distilled  water,  if  carefully 
done,  overcome  the  former,  and  we  think  that,  in  regard  to  the 
latter,  very  little  action  takes  place  if  the  temperature  is  kept  at 
130°  Tahr.  It  is  important,  furthermore,  in  this  case,  to  use  only 
litmus  as  indicator. 

The  lecturer  has  pointed  out  the  important  part  played  by 
iron  salts  in  the  degradation  of  papers.  Iron  salts,  like  salts  of 
alumina,  are  withdrawn  from  solution  by  the  fibre.  They  both, 
we  believe,  readily  undergo  dissociation  into  acid  and  base  in  the 
fibre. 

There  is  conclusive  evidence  of  this  in  the  ease  of  iron  salts, 
and  it  is  extremely  probable  in  the  case  of  alumina.  Both  the 
bases  formed,  namely,  ferric  oxide  and  alumina,  are  insoluble,  but 
the  dissociated  acid  may  enter  into  solution  and  be  removed  by 
washing,  leaving  the  pulp  basic.  The  iron  base  has  the  power  of 
oxidising  and  weakening  the  fibre  by  abstracting  oxygen  from  the 
atmosphere  and  giving  it  up  to  the  fibre.  It  is  probable  that 
alumina  has  this  power  also,  but  in  a  much  less  degree.  This 
action  takes  place  most  readily  when  the  material  is  slightly 
moistened  and  exposed  to  the  atmosphere. 

The  effects  of  iron  and  copper  salts  upon  cellulose  at  higher 
temperatures  can  easily  be  illustrated,  especially  the  former.  An 
ordinary  india-rubber  stamp  if  moistened  by  pressing  upon  a  pad 
impregnated  with  a  solution  containing  one  part  of  ferrous  sul¬ 
phate  per  1,000  of  water,  and  then  pressed  upon  a  sheet  of  paper, 
leaves  no  discoloration  when  the  same  is  allowed  to  dry.  If, 
however,  the  paper  is  placed  at  some  distance  from  a  flame,  so  as 
to  allow  it  to  get  hot  without  charring,  the  device  imprinted  on 
the  paper  quickly  develops  up  in  sharp  outline.  The  heat  appears 
to  disengage  an  almost  infinitesimal  quantity  of  ferric  oxide, 
which,  in  its  extremely  finely  divided  state,  acts  as  a  conveyer  of 
oxygen  to  the  paper  and  chars  it  wherever  the  salt  has  been 
allowed  to  come  in  contact.  The  same  experiment  should  be  tried 
with  a  copper  salt  and  with  acetate  of  alumina. 

The  above  experiments  are  convincing  that  the  presence  of 
such  bases,  when  even  in  minute  quantity,  are  liable  to  degrade 

D 


98 


papers  considerably  in  hot  climates.  It  appears  also  probable 
that  in  a  very  damp  climate  salts  of  these  bases  act  as  bearers  of 
oxygen  and  in  some  cases  the  bases  themselves. 

The  above-described  methods  for  the  determination  of  the 
basicity  of  a  paper  give  no  indication  as  to  what  bases  are 
present.  The  iron  salts  are  more  liable  to  dissociation  than  the 
salts  of  alumina,  and  are  more  to  be  feared  hi  large  quantities 
on  account  of  their  destructive  action. 

The  presence  of  such  bases  as  these  have  an  important 
influence  upon  a  paper’s  qualities  for  taking  different  colouring 
matters.  Many  colouring  matters  form  an  insoluble  lake  with 
alumina;  this  in  all  probability  adds  to  the  fastness  and  per¬ 
manence  of  the  colour,  but  often  considerably  alters  its  shade  from 
that  of  the  original.  Some  aniline  colours  also  will  not  stand 
the  presence  of  bases,  whilst  others  will  not  stand  acid  constituents. 

A  great  deal  of  trouble  is  often  experienced  with  printing 
inks  and  some  kind  of  paper,  which  can  be  traced  to  these  con¬ 
stituents,  which,  although  present  often  in  minute  quantities 
only,  are  sometimes  capable  of  exerting  a  very  powerful  and 
destructive  influence. 

I  have  seen  it  stated,  in  some  cases,  that  chlorides  are 
destructive  wdien  present  even  as  a  chemical  residue  in  papers. 
I  believe  that  some  chlorides  are,  such  as  chlorides  of  alumina,  and 
that  their  destructive  action  is  due  to  dissociation,  which  takes 
place  within  t  he  fibre,  but  I  should  hardly  think  that  chloride  of 
sodium,  or  common  salt,  is  destructive,  at  least  as  a  residue. 
This  is  a  question,  however,  on  which  we  have  very  little 
knowledge. 

We  will  now  deal  with  the  potassium  iodide  test  in  its  appli¬ 
cation  to  paper,  and  you  will  see,  I  think,  if  you  follow  my 
arguments,  that  any  inferences  and  deductions  can  only  be  arrived 
at  after  a  thorough  knowledge  of  all  the  conditions  and  of  the 
chemical  changes  that  take  place  when  the  conditions  are  varied. 

Mr.  E.  Hughes,  in  a  paper  on  “  Water  as  a  Catalyst”  (Phil. 
Mag.  (v.),  35,  531-534),  remarked  that  paper,  when  moistened 
with  potassium  iodide  solution  and  exposed  to  the  light,  assumes 
a  brownish-violet  tint.  As  the  staining  varies  very  greatly  with 
different  kinds  of  paper,  being  greatest  with  highest  glazed  note- 
paper,  he  attributes  it  to  the  presence  of  chlorine  in  the  paper. 
Hughes  studied  this  reaction  from  the  point  of  view  of  the 
moisture  acting  in  some  way  as  a  promoter  of  chemical  change. 
We  desire  to  regard  it  solely  from  the  point  of  view  of  the  paper 
itself. 


99 


There  are  several  other  explanations  of  this  peculiar  reaction 
which  appear  to  be  far  more  probable  than  that  given  above. 
The  potassium  iodide  may  contain  potassium  iodate,  and  free 
iodine  may  be  liberated  by  the  action  of  the  alum  contained  in 
the  paper  in  these  substances.  As  paper  almost  invariably  con¬ 
tains  starch,  we  should  expect  to  find  that  the  colour  produced 
was  more  of  a  deep  blue,  due  to  the  action  of  the  free  iodine  in 
the  starch  of  the  paper.  If,  however,  paper  containing  starch  be 
dipped  into  a  weak  iodine  solution,  so  as  to  produce  a  deep  blue 
colour,  this,  on  exposure  to  bright  sunlight,  is  very  rapidly  dis¬ 
charged.  In  this  case  there  appears  to  be  very  little  doubt  that 
the  iodine,  in  combination  with  the  starch,  is  converted  by  the 
action  of  moisture  contained  in  the  paper  into  hydriodic  acid, 
and  that  oxygen  is  liberated. 

In  the  case  of  paper  moistened  with  potassium  iodide,  the 
production  of  a  colour  seems  rather  to  indicate  that  iodine  is  in 
some  way  liberated,  but  that  it  is  not  converted  into  visible  hydri¬ 
odic  acid  as  the  moisture  is  evaporated  from  the  surface  before 
there  is  time  for  this  action  to  take  place.  Free  iodine  cannot 
be  formed  by  the  action  of  an  acid  upon  potassium  iodide  unless 
it  also  contain  iodate.  It  is  possible  that  some  iodate  is  formed 
by  the  oxidation  of  the  atmosphere,  and  that  if  the  paper  is  of  an 
acid  nature  free  iodine  may  then  be  liberated.  Supposing  this 
to  be  true,  in  what  way  would  the  character  of  the  paper  used 
affect  this  change?  Hughes  found  that  the  stain  produced  is 
greatest  with  highly -glazed  notepaper.  It  seems  hardly  probable 
that  the  explanation  last  given  can  account  for  the  staining, 
since  highly-glazed  notepaper  is  about  the  least  likely  to  give  an 
acid  reaction.  There  are  good  grounds  for  this  statement.  For 
many  months  the  lecturer  examined  daily  about  ten  samples  of 
writing  paper  quantitatively  for  chemical  condition,  of  which 
a  record  was  kept,  together  with  particulars  of  chemicals  added  to 
furnish.  Out  of  the  whole  lot  of  papers  examined  there  is  not  a 
single  instance  of  paper  containing  free  acid.  Although  many  of 
the  papers  gave  an  acid  reaction  to  litmus,  none  were  acid  to 
methyl  orange,  showing  that  the  alum  is  always  in  a  basic  con¬ 
dition.  Many  of  them  are  alkaline  even  to  litmus,  especially 
those  which  are  tub-sized  only  and  made  in  districts  where  the 
water  is  hard. 

I  am  doubtful  whether  alum  alone  would  liberate  iodine  ;  it 
might  do,  the  conditions  being  peculiar.  Highly-glazed  notepaper 
being  most  liable  to  staining  under  these  conditions  seems  to 
imply  quite  a  different  cause  than  that  given  above.  With  papers 

n  2 


100 


of  this  description,  when  moistened  with  potassium-iodide 
solution,  it  appears  that  the  air  in  contact  with  the  paper  would 
have  its  maximum  effect,  since  most  of  the  solution  is  on  the 
outside  of  the  paper,  as  it  were.  AVith  a  soft  paper,  the 
solution  would  be  absorbed  more  into  its  body,  and  if  the  alum 
promoted  this  change,  we  should  expect  it  to  do  so  more  rapidly 
in  the  latter.  If,  on  the  other  hand,  wre  assume  that  chlorine  in 
the  paper  is  the  cause,  we  would  expect  the  latter  to  be  more 
stained,  since  it  is  more  thoroughly  permeated  by  the  liquid.  It 
is  impossible,  in  my  opinion,  for  chlorine  or  hypochlorites 
to  be  present  in  the  paper,  as  they  are  quickly  oxidised  by 
the  atmosphere ;  nor  is  it  possible  for  the  chlorine  present  in 
the  paper,  in  the  form  of  chloride,  to  liberate  the  iodine  from 
potassium  iodide. 

Although  it  cannot  at  present  be  proved,  the  only  explanation 
of  this  staining  appears  to  me  to  be  as  follows  : — The  atmosphere 
contains  both  ozone  and  hydrogen  peroxide,  both  of  which 
have  the  power  of  liberating  iodine  from  a  solution  of  potassium 
iodide.  So  long  as  moisture  is  present  this  liberation  can  be 
effected,  and  is  probably  greatly  accentuated  when  using  paper 
as  a  medium.  The  action  is  greater  in  the  light,  as  those 
substances  are  more  abundant  in  the  light.  The  iodine  so  liberated 
may  enter  into  combination  with  the  starch,  and  when  the 
paper  is  dry  no  further  action  takes  place.  This  appears  at  first 
sight  not  to  agree  with  the  statement  that  the  iodine-starch 
colour  is  discharged  on  placing  the  paper  in  bright  sunlight. 
But  I  think  there  is  no  difficulty  in  explaining  this  on 
the  same  assumption.  Ozone  may  complete  the  change.  It 
probably  takes  place  according  to  the  following  equation  : — 

I2  +  H20  =  2HI  +  0 

Ozone  may  promote  the  change  by  the  withdrawal  of  oxygen 
from  the  water,  converting  the  ozone  into  common  oxygen — 

Os  +  O  =  202 

As  a  proof  that  this  change  does  not  depend  upon  the  composition 
of  the  paper  itself  or  anything  contained  in  the  paper,  starch 
alone,  after  treating  with  iodine  to  produce  this  blue  colour, 
fades  similarly  under  the  action  of  bright  sunlight. 

Iodine  has  been  used  in  paper  as  potassium  iodide,  together 
with  starch,  as  a  means  of  estimating  the  amount  of  ozone  in 
the  atmosphere,  by  noting  the  amount  of  colour  produced  for  a 
given  time  of  exposure.  It  has  proved  itself  to  be  altogether 
unreliable,  as  might  well  be  inferred  from  what  has  been  above 
stated.  The  presence  of  nitric  acid  in  the  air  also  tends  to 


101 


produce  this  discoloration.  We  must,  therefore,  regard  it  as  being 
a  very  mixed  reaction. 

Paper  containing  starch  and  immersed  in  a  dilute  solution 
of  iodine  changes  to  a  blue  colour  in  proportion  to  the  amount  of 
starch  present.  If  this  paper  be  half  immersed  in  the  solution, 
it  will  be  found  that  that  portion  still  kept  damp,  but  exposed 
to  the  air,  loses  its  colour  much  more  readily  than  the  immersed 
portion.  In  fact,  the  latter  does  not  become  white  again  until 
the  solution  has  lost  its  free  iodine  by  contact  with  the  atmosphere. 

Some  of  the  questions  raised  in  this  lecture  are  rather 
abstruse,  at  any  rate  for  the  ordinary  student,  but  they  are 
worthy  of  careful  consideration  by  the  paper  mill  chemist.  I 
can  hardly  expect  many  to  assimilate  all  that  is  here  set  forth.  I 
have  given  it  partly  because  it  should  prove  of  some  value  to 
those  who  have  to  prepare  papers  for  special  purposes,  such  as 
drawing  and  pei’haps  photograph  papers,  and  such  papers  that 
have  to  stand  some  of  our  fugitive  inks.  I  have,  however, 
another  object  in  bringing  this  matter  forward,  and  that  is  to  show 
those  who  are  in  the  habit  of  applying  rough-and-ready  tests  to 
papers  and  drawing  hasty  conclusions  that  a  little  knowledge  is 
dangerous.  And  I  do  this  not  without  some  reason,  because  cases 
have  come  under  my  notice  more  than  once  of  absurd  tests  having 
been  applied,  and  still  more  absurd  conditions  having  been 
imposed,  in  contracts  which  are  thought  to  be  a  safeguard  as  to 
composition  of  paper,  but  in  effect  prove  to  be  vexatious 
impositions  and  devoid  of  all  reason.  If  those  stationers  and 
printers  who  wish  to  make  conditions  in  their  contracts  for  the 
purpose  of  safeguarding  themselves  against  any  chemical  residues 
which  might  prove  harmful  either  to  the  paper  itself  or  to  the 
inks  used  upon  it  would  consult  some  authority  who  has  made  a 
study  of  the  subject,  both  from  the  maker’s  and  the  printer’s  point 
of  view,  some  satisfactory  and  practical  test  might  be  devised, 
which,  besides  being  effective,  might  in  no  way  prove  vexatious 
to  either  party. 


LECTURE  VIII. 


THE  FUNCTION  OF  WATER  IN  THE  FORMATION 
OF  A  WEB  OF  PAPER. 

Effects  of  water  on  fibres — Flexibility — Felting  qualities — Elasticity — 
Shrinkage  on  drying — Removal  of  water — Influence  of  temperature  when 
hydraulic  pressing — Capillarity— Brittleness — Effects  of  rosin — Beating — 
Calendering — Physical  properties  of  fibres. 


In  a  previous  lecture  an  attempt  has  been  made  to  show 
that  water  has  a  very  important  duty  to  perform  in  the  felting 
of  fibres  for  the  production  of  a  sheet  of  paper.  An  early  writer, 
who  described  paper  as  being  an  aqueous  deposit  of  a  fibre,  gave  a 
somewhat  inadequate  definition,  and  only  partially  revealed  its 
real  nature.  It  would  be  better  perhaps,  and  for  reasons  that 
will  be  more  evident  when  the  real  functions  of  water  are 
correctly  stated,  to  define  paper  as  an  aqueous  deposit  of  any 
vegetable  fibre.  As  far,  at  any  rate,  as  this  lecture  is  concerned, 
we  will  accept  this  definition,  as  my  remarks  can  only  be  said  to 
apply  to  paper  of  vegetable  origin. 

When  an  ordinary  waterleaf  is  wetted,  it  not  only  expands, 
but  becomes  also  very  much  weakened,  so  that  it  will  often 
fall  to  pieces  when  held  between  the  fingers.  This  change  in 
strength  that  paper  undergoes  on  assimilation  of  water  is  the 
result  of  the  action  of  the  water  upon  the  ultimate  fibres  of 
which  the  paper  is  composed,  and  it  will  be  necessary  to 
investigate,  this,  y,ery,  c,arefully  ill.  ordhfr  thqt  .we  may  understand 
the  chief , part  that  water  plays  in(its  iormatiop. 

I  shall  endeavour  to  show  that  the  effect  of  water  upon 
cellulpse  .fibres  is- £<?  •  give  them  ipcrea^dnfiexibrl'ity^.Vhich  allows 
of  the;  fihsefe.  being  .dravtn  alpart.  wi'cH  f.drrtpaVative-  ease  when 


103 


unsized  waterleafed  paper  is  wetted.  Conversely,  in  the  pro¬ 
duction  of  paper,  the  fibres  at  the  start  exhibit  their  greatest 
flexibility  and  pliability  as  they  are  suspended  in  a  watery 
medium.  In  the  process  of  the  formation  of  the  web  they  are 
first  of  all  deposited  so  as  to  interlace  one  with  the  other,  and,  in 
course  of  treatment,  become  more  stubborn  and  resistant  by  the 
removal  of  water  until,  when  air-dry,  the  paper  has  gained  its 
maximum  strength. 

It  is,  so  far  as  I  know,  impossible  to  examine  the  ultimate 
fibres,  say,  of  cotton,  linen,  or  of  wood,  for  varying  degrees  of 
flexibility  under  the  influence  of  moisture,  but  it  is  possible  to 
obtain  a  mass  of  amorphous  cellulose,  we  have  every  reason  to 
believe,  closely  allied  in  general  physical  properties  to  that  which 
constitutes  the  cell-wall  of  the  ultimate  fibres,  and  from  the 
physical  behaviour  of  such  amorphous  cellulose  the  general 
deportment  of  fibres  under  similar  treatment  may  be  inferred. 

Sheets  of  amorphous  cellulose,  possessing  in  the  aggregate 
the  properties  of  the  cotton  fibre,  may  be  obtained  by  heating 
down  to  dryness  on  a  glass  plate  a  solution  of  cellulose  thio- 
carbonate.  After  washing,  a  flexible  sheet  of  cellulose  is  obtained 
which  can  be  examined  for  flexibility  under  varying  conditions  of 
moisture.  The  film  itself  varies  in  properties  according  to  its 
mode  of  preparation.  This  fact  seems  to  indicate  that  ultimate 
fibres  vary  in  the  same  way  according  to  their  mode  of  elaboration. 
The  property  which  concerns  us  most  is  that  of  flexibility,  and 
this  can  be  made  to  vary  at  will  by  altering  the  conditions  of 
setting  the  cellulose  from  its  compounds  in  solution.  From  this 
“  elastic  ”  property  of  cellulose  the  difference  in  the  elasticity  of 
various  ultimate  vegetable  fibres  may  be  inferred  by  which  an 
explanation  is  afforded  of  their  great  differences  in  felting  power. 

Cellulose  films  may  be  obtained  as  above  described  that 
are  tough  and  rigid  when  in  a  dry  atmosphere;  but  when  placed 
in  a  damp  atmosphere  they  become  remarkably  flexible,  and  on 
immersion  in  water  possess  the  pliability  of  a  sheet  of  rubber. 
Films,  on  the  other  hand,  may  be  obtained,  by  altering  the 
conditions  of  preparation,  that  exhibit  only  a  slightly  increased 
flexibility  on  exposure  to  a  damp  atmosphere  or  immersion  in 
water.  A  film  may  also  be  obtained  that  when  dry  is  extremely 
brittle,  so  much  so  that  it  will  fly  to  pieces  spontaneously,  or 
when  slightly  scratched  on  the  surface.  It  is  cellulose  of  this 
nature  that  exhibits  the  greatest  range  of  flexibility  when  acted 
on  by  moisture.  It  appears  from  the  study  of  amorphous 
cellulose  towards  absorption  in  water  that  the  particles  have, 


104 


as  it  were,  a  certain  elasticity,  and  the  removal  of  water  by  heat 
causes  the  particles  to  come  close  together,  and  that  whilst  in 
close  contact,  due  to  the  removal  of  water  by  heat  and  such 
means,  the  particles  are  in  a  state  of  tension.  This  appears  to 
account  for  the  brittle  nature  of  the  material  when  the  water  is 
removed  by  heat.  When  this  is  brought  in  contact  with  water 
it  expands  to  a  certain  degree,  taking  up  water  and  recovering 
its  elasticity.  It  appears,  then,  that  the  greater  the  tension  in 
the  dry  substance  the  greater  its  affinity  for  water,  and  hence  the 
most  brittle  substance  when  dry  is  most  pliable  when  wTet. 

If  the  water  be  removed  from  tbe  substance  by  compression 
in  the  first  instance,  the  particles  are  brought  permanently  into 
close  contact,  and  being  free  from  tension  they  have  no  desire  to 
take  up  water.  The  material  partakes  of  this  nature  in  pro¬ 
portion  to  the  compression.  Material  so  prepared  is  tough  and 
rigid  when  dry,  and  preserves  this  property  in  a  measure  when 
wetted.  It  neither  expands  nor  assimilates  moisture  when 
wetted  to  anything  like  the  degree  of  the  former  preparation. 
The  cell-wall  of  an  ultimate  fibre  consists  of  cellulose  which  is 
more  closely  allied  to  one  or  other  of  the  above,  according  to  the 
conditions  of  its  elaboration.  Some  fibres,  it  will  be  noticed, 
produce  a  very  strong  paper,  which  shrinks  enormously  on  drying. 
The  strength  of  a  paper  cannot,  however,  be  taken  as  a  measure 
of  the  felting  properties  of  the  constituent  fibres,  as  the  length 
of  the  fibres  has  a  lot  to  do  with  the  strength  of  the  paper.  A 
small  amount  of  moisture  is  often  sufficient  to  materially  affect 
the  strength.  Paper,  when  put  in  a  testing  machine,  and  under 
a  moderate  amount  of  strain,  easily  breaks  asunder  if  the  finger  is 
moistened  and  drawn  across  it.  The  strength  is  materially 
lessened  even  by  breathing  on  the  surface  when  under  strain. 

We  see  then  that  it  is  altogether  a  mistake  to  assume  that 
water  acts  merely  as  a  medium  in  which  the  fibres  are  suspended. 
The  fibres  expand  by  taking  up  water,  and  the  amount  that  they 
take  up  is  dependent  upon  the  moistness  of  their  surroundings. 
Their  flexibility  is  in  proportion  to  their  expansion,  and  therefore 
to  the  amount  of  water  present. 

In  the  form  of  pulp  the  fibres  contain  their  maximum  of 
water,  and  therefore  exhibit  their  maximum  flexibility.  The  first 
part  of  the  water  is  removed  by  gravitation  ;  this  cannot  affect  the 
flexibility  of  the  fibres.  The  next  portion  of  water  is  removed  by 
pressure  ;  this  is  probably  insufficient  to  affect  the  flexibility,  but 
makes  the  web  somewhat  stronger  by  causing  the  fibres  to  lay 
closer.  The  water  removed  by  these  two  processes  is  the  surplus 


105 


water  in  which  the  fibres  have  been  suspended.  The  amount  of 
water  really  assimilated  by  the  fibres  themselves,  by  which  their 
volume  is  augmented,  is  relatively  only  a  very  small  quantity  of 
that  used  m  the  pulp,  probably  only  about  one-fortieth 
and  sometimes  very  much  less.  The  fibi’es,  on  immersion, 
in  some  cases  may  expand  to  double  their  dry  volume.  In  doing 
so,  they  would  absorb  about  three-fourths  their  weight  of  water. 
The  web,  after  passing  the  second  press-rolls,  contains  on  an 
average  about  four  times  its  weight  of  water,  or  more  than  five 
times  the  water  necessary  for  the  hydration  of  the  cellulose. 
As  the  web  passes  on  to  the  drying  cylinders  the  surplus  water 
passes  off,  first  being  converted  into  steam.  As  this  goes  on,  the 
cellulose  becomes  dehydrated  by  giving  up  its  water.  This 
appears  at  first  as  sensible  moisture,  merely  separating  from  the 
cellulose ;  it,  however,  quickly  becomes  vaporised  by  the  heat,  but 
produces  the  sense  of  dampness  to  the  web  so  long  as  it  is  being 
emitted. 

Here  we  touch  upon  another  question,  namely,  that  of  the 
effect  of  water  of  different  temperatures  upon  the  flexibility  and 
expansion  of  cellulose.  This  question  has  an  important  bearing 
upon  that  of  the  stuff  working  “wet”  or  “free”  on  the  machine, 
also  one  closely  allied  to  this — the  removal  of  water  from  paper 
stock  by  hydraulic  pressure.  We  have  to  appeal  again  to  the 
properties  of  amorphous  cellulose  sheets  or  blocks  under  similar 
conditions.  Supposing  we  put  into  co^l  water  a  mass  of  the 
cellulose  material  beforementioned  that  has  been  previously  dried 
by  heat,  and  wait  till  it  has  taken  up  as  much  water  as  it  will,  we 
weigh  it  and  find  it  has  doubled  in  weight.  If  we  then  put  it 
into  warm  water  and  allow  it  to  remain  for  some  time,  it  will 
contract  and  be  found  to  weigh  less.  It  will  weigh  less  and 
contract  more  the  higher  the  temperature  of  the  water.  There  is 
every  reason  to  believe  that  ultimate  fibres  behave  in  a  similar 
way.  In  hydraulic  pressing  paper  stock  with  well-beaten  rag- 
stuff  by  the  application  of  300  lbs.  per  square  inch  for  the  pro¬ 
duction  of  cakes  15  inches  in  diameter  by  5  inches  deep,  if  cold 
water  be  used  the  moisture  after  pressing  contains  about  50  per 
cent,  of  water  and  50  per  cent,  of  air-dry  fibre.  It  is  well 
known  that  it  requires  a  very  great  increase  of  pressure  to  obtain 
a  mixture  perceptibly  drier  than  this.  It  appears  that  this 
amount  of  water  is  fairly  bound  by  the  fibre  itself.  Supposing, 
now,  that  the  paper  pulp  is  pressed  whilst  very  hot,  the  water  is 
found  to  drain  away  with  much  greater  ease,  and  a  moisture  is 
easily  obtained  containing  40  per  cent,  water  and  60  per  cent. 


106 


air-dry  fibre.  Notice  this  confirms  my  former  statement,  namely, 
that  fibres  absorb  about  three-fourths  their  weight  of  water, 
which  is  taken  up  by  the  cell-wall  and  gives  the  fibres  their 
increased  bulk  and  flexibility  on  immersion.  I  would  put  it  this 
way :  the  fibres  in  a  watery  medium  take  up  100  per  cent,  in  the 
cold  or  67  per  cent,  when  the  liquid  is  hot.  This  affords  an 
explanation  of  the  difference  in  the  behaviour  of  stuff  on  the 
machine  when  heated.  Also  it  helps  to  explain  why  heat  tends 
to  make  “  wet  ”  stuff  work  free,  and  it  merely  comes  to  this — 
heat  tends  to  dehydrate  cellulose. 

This  difference  cannot  be  due  to  the  expansion  of  the  water  as 
water ;  there  is  only  a  difference  of  5  per  cent,  between  cold  and 
boiling  water ;  this  would  only  make  a  difference  of  2  per  cent, 
in  the  composition  of  the  pressed  mass.  The  only  true 
explanation  appears  to  be  that  the  fibres  contract  in  the  hot 
water,  and  therefore  retain  a  less  quantity  of  water  than  when 
cold. 

The  cellulose  is  converted  into  cellulose  hydrate  by  beating. 
The  hydrate  is  higher  when  the  beating  is  prolonged.  On  raising 
the  temperature  of  the  stuff  the  cellulose  is  dehydrated,  and  the 
extent  to  which  it  is  dehydrated  is  dependent  upon  the  tempera¬ 
ture  through  which  it  is  raised.  The  surplus  water  that  is  not 
in  chemical  union  as  hydrate  is  easily  removed  by  pressure ; 
greater  pressure  is  required  to  dehydrate.  It  follows,  then,  that 
on  a  paper  machine,  only  that  portion  of  the  water  that  is  not 
combined  with  the  cellulose  is  removed  by  pressure,  the  combined 
water  being  removed  by  heat  in  the  drying  cylinders. 

With  regard  to  the  working  of  the  stuff  on  the  endless  wire 
of  the  paper  machine,  the  problem  is  very  much  more  complex. 
The  contraction  of  the  fibres  per  ,ie  cannot  account  for  the 
readiness  with  which  the  water  leaves  the  wire.  The  difference 
in  the  temperature  is  only  a  matter  of  40°  Fahr.  at  the  outside, 
and  the  water  retained  in  either  case  is  tenfold  that  assimilated 
by  the  fibre  itself.  It  appears  rather  that  what  is  known  as  the 
capillarity  of  the  fibre  is  decreased.  By  capillarity  is  meant  the 
power  of  taking  up  a  liquid  as  a  wick  soaks  up  oil.  The  decreased 
volume  of  the  fibre  is  accompanied  by  a  decreased  power  of  soaking 
up  the  liquid,  it  therefore  runs  off,  like  water  off  a  duck’s  back, 
having  less  affinity.  Bodies  of  the  nature  of  alkali  retain  surplus 
water  in  proportion  as  they  become  softened  and  hydrated  by  the 
assimilation  of  water.  Nitro-celluloses,  such  as  gun-cotton, 
retain  little  water  after  draining;  this  is  largely  due  to  the  fact 
that  their  fibres  are  rigid,  and  have  lost  that  pliability  by  which 


107 


the  small  fibres  are  enabled  to  seal  up  the  small  holes  which  allow 
of  the  escape  of  water. 

As  the  fibres  are  rendered  more  rigid  and  inflexible  by  the 
increase  in  temperature  of  the  water  medium,  they  lay  one  upon 
the  other  in  the  web,  more  like  a  number  of  sticks  or  bavins  than 
a  mass  of  flexible  fibres. 

It  is  easy  to  see  that  such  a  mass  would  allow  of  the  escape  of 
water  with  much  greater  freedom.  This,  probably,  is  of  valuable 
aid  to  us  in  manipulating  the  stuff  on  the  “wet-end”  of  the 
machine.  By  regulating  the  temperature,  the  stuff  may  be  made 
to  work  “  free  ”  or  “  wet  ”  at  will. 

We  next  come  to  consider  why  the  stuff  is  caused  to  work 
wet  by  being  left  long  in  the  chest  or  in  the  engine.  The 
effect  of  water  upon  cellulose  is  far  from  being  instantaneous. 
The  cellulose  composing  the  cell-wall  of  a  fibre  cannot  be 
regarded  as  being  uniform  in  constitution.  It  consists  of  an 
exterior  that  is  much  more  resistant  to  all  sorts  of  chemical 
attack  than  the  interior.  If  the  unbroken  ultimate  fibres  be 
suspended  in  water,  their  softening  and  expansion  is  much  more 
gradual  than  if  the  same  had  been  cut  into  several  pieces  by  the 
action  of  the  beater  roll.  In  the  latter  case,  all  parts  of  the  fibre 
are  exposed  to  the  action  of  the  water.  This  appears  to  account 
for  stuff  working  very  wet  when  kept  long  in  the  beater.  If 
kept  very  long  in  the  chest,  the  long-continued  action  of  the 
water  penetrates  the  outer  covering,  and  more  thoroughly 
expands  and  softens  the  fibre. 

When  paper  is  hard-dried  by  exposure  to  a  temperature 
of  220°  Fahr..  which  is  sufficient  to  drive  off  all  the  hygroscopic 
moisture,  it  often  is  found  to  be  quite  brittle.  This  is  probably 
due  to  the  fact  that  the  cellulose  composing  the  cell- wall  of  the 
fibres  is  in  a  state  of  tension,  due  to  the  removal  of  water ;  as  with 
the  film  of  amorphous  cellulose  the  strength  is  restored  when  it 
regains  moisture,  unless  the  qualities  of  the  cellulose  are 
permanently  impaired  by  oxidation  at  this  temperature. 

The  surface  of  a  glazed  paper  is  soon  removed  by  moistening. 
This  is  due  to  the  expansion  of  the  fibres.  When  the  fibres  are 
dry,  although  often  brittle,  they  partake  somewhat  of  the  nature 
of  metal,  and  admit  of  a  bright  polished  surface  by  the  application 
of  pressure  or  friction.  On  wetting,  the  fibres  first  of  all  regain 
a  certain  amount  of  elasticity  which  they  had  lost  when  very  dry. 
They  stand  up  and  come  apart  to  a  certain  extent,  and  undo  the 
effects  of  the  pressure.  Paper  can  be  smoothed  on  its  surface,  but 
not  highly  glazed  when  damp,  for  this  reason  ;  also  paper,  on 


108 


account  of  its  brittleness  when  very  dry,  is  much  more  likely  to 
be  crushed  under  the  action  of  the  glazing  rolls. 

With  rosin-sized  papers,  the  ease  with  which  they  part,  when 
re-wetted,  is  no  measure  of  the  pliability  of  the  fibres,  as  they  are 
cemented  together  with  rosin,  which  is  not  affected  by  the  water. 
The  cementing  by  the  rosin  is  done  as  the  paper  passes  over  the 
drying  cylinders.  The  re-wetted  paper,  therefore,  is  much 
stronger  than  the  paper  with  the  same  degree  of  moisture  before 
the  same  has  passed  over  the  drying  cylinders. 

We  have  already  seen  that  dry  amorphous  cellulose  may  so 
be  prepared  as  to  fly  to  pieces  when  the  surface  is  merely 
scratched.  When  this  is  brought  into  contact  with  water,  it 
expands  to  a  certain  degree,  taking  up  water,  and  recovei’s  its 
elasticity,  and  is  no  longer  brittle.  If,  however,  the  moisture 
is  removed  by  forcing  the  particles  together  under  high  pressures, 
the  cellulose  is  not  brittle  and  expands  less  on  immersion.  It 
appears  probable  that  similar  stresses  are  set  up  in  the  ultimate 
fibre,  and  that  these  vary  according  to  the  conditions  under 
which  the  cellulose  has  been  elaborated  in  the  living  plant. 
These  are  stresses  set  up  when  the  cell  is  deprived  of  moisture, 
and  only  relieved  when  the  moisture  is  allowed  to  re-enter.  In 
the  case  of  an  amorphous  film  of  cellulose,  prepared  so  that  it  is 
capable  of  considerable  expansion  when  wetted,  the  water  appears 
to  enter  into  some  sort  of  chemical  union  with  the  cellulose,  or 
to  be  dissolved  or  solidified  by  it.  The  hygroscopic  moisture 
appears  to  bear  some  direct  relationship  with  the  absorption  of 
water  on  immersion.  That  water  is  essential  to  these  change's 
is  apparent  when  we  use  any  other  liquid.  We  are  all  surprised 
to  find,  for  instance,  that  paper  retains  its  dry  feel  when  immersed 
in  very  strong  alcohol.  It  also  retains  its  strength,  as  there  is 
no  water  present  to  produce  any  flexibility  of  the  fibres.  It  is 
possible  that  the  firmness  of  a  paper  is  actually  increased  under 
absolute  alcohol,  as  the  liquid  has  the  power  of  withdrawing  even 
the  hygroscopic  moisture  of  the  paper,  just  as  though  it  had  been 
placed  in  an  air-bath.  The  behaviour  of  vegetable  fibres  suspended 
in  a  medium  of  strong  alcohol  demonstrates  that  they  have  lost 
their  felting  power.  Other  liquids  may  be  used,  such  as  ether  or 
carbon  bisulphide,  with  similar  results.  The  felting  power  of  the 
fibres  in  presence  of  water  is  not  then  due  to  the  fact  that 
they  are  in  presence  of  an  inert  liquid  medium,  but  that  they 
are  suspended  in  a  medium  which  has  a  powerful  influence  upon 
their  physical  and  chemical  constitution.  The  only  liquid,  as 
far  as  I  am  aware,  that  could  exercise  this  influence  is  water. 


109 


The  question  as  to  whether  fibres  stick  together  on  drying  in 
contact  is  worthy  of  consideration.  Is  it  possible  that  there 
can  be  some  substance  of  a  glutinous  nature  affected  by  water  that 
causes  the  fibres  to  adhere  when  dry  ?  I  think  there  is  every  reason 
to  believe  that  no  such  substance  can  exist.  If  such  substance 
existed,  it  would  probably  be  capable  of  separation  from  the 
cellulose  of  the  fibre.  Prom  the  manner  in  which  dry  paper 
tears,  it  appears  rather  that  the  interlacing  of  the  fibres  is 
responsible  for  the  strength,  than  that  it  can  be  due  to  any 
glutinous  materials. 

The  views  above  expressed  as  to  the  function  of  water  in  the 
formation  of  a  web  of  paper  agree  closely  with  what  is  noticed 
in  practice.  Pibres  which  have  a  tendency  to  work  “  wet  ”  are 
generally  those  which  have  the  greatest  shrinkage,  and  result  in 
the  production  of  the  strongest  papers. 

The  effect  of  long  beating  or  long  standing  in  the  chest 
is  to  produce  wet  stuff  with  an  increased  shrinkage  in  the  web. 
Heat  applied  to  the  stuff  before  passing  on  to  the  wire  tends  to 
make  the  stuff  work  “  free.”  The  shrinkage  in  the  web  is  found 
to  be  greater  when  the  stuff  has  laid  for  a  long  time  in  the  chest, 
as  on  Monday  morning. 

Por  the  production  of  very  strong  papers,  such  as  “banks,” 
it  is  customary  to  leave  the  stuff  for  a  long  time  in  the  engine. 
One  object  of  this  is  to  brush  the  stuff  out,  so  as  to  leave  the 
fibres  intact.  The  effect  that  it  also  has,  however,  is  to  cause 
the  stuff  to  work  wet  by  the  increased  assimilation  of  water  by  the 
fibres,  which  results  in  their  increased  flexibility. 

The  paper  produced  is  better  felted,  it  has  a  greater 
shrinkage,  and  is  stronger. 

Many  fibres  after  bleaching  are  condemned,  entirely  on 
account  of  the  stuff  working  too  wet  to  be  run  on  the  machine. 
In  the  case  of  one  fibre  which  I  found  to  work  very  “  wet,”  I 
obtained  a  sheet  which  showed  a  shrinkage  of  30  per  cent,  in 
one  direction  on  drying.  The  paper  obtained  was  exceedingly 
hard  and  tough,  but,  in  spite  of  the  good  qualities  of  the  paper 
produced,  the  raw  material  was  condemned  as  being  impossible 
to  run  over  the  machine  at  a  sufficient  rate  to  make  it  pay. 

The  condition  of  a  fibre  in  this  respect  is  largely  dependent 
upon  the  way  it  is  beaten.  Beating  has  become  quite  a  fine  art, 
also  the  construction  of  beaters  suitable  for  the  production  of 
stuff  adapted  to  any  specific  purpose.  Some  years  ago  it  was 
thought  that  a  certain  paper  possessing  certain  qualifications 
would  have  to  be  made  from  certain  raw  materials.  It  is  now 


no 


becoming  widely  recognised  that  the  manipulation  of  the  stuff  in 
the  beating  and  in  the  other  mechanical  processes  is  an  ever- 
increasing  factor.  Wood  may  be  made  to  partake  somewhat  of 
the  nature  of  cotton,  and  cotton,  in  a  less  measure,  perhaps,  of 
the  nature  of  wood.  Wood  may  also  be  made  to  replace  either 
linen,  for  the  manufacture  of  strong  banks,  or  it  may  be  made  soft 
and  spongy  suitable  for  illustrated  papers  and  litho  work.  It  must 
not  be  forgotten,  however,  that  the  chemical  treatment  preparatory 
to  the  beating  has  a  wonderful  influence  upon  the  condition  of  the 
fibres ;  but  this,  again,  leaves  the  fibres  with  more  or  less  affinity 
for  water. 

It  stands  to  reason  that  it  is  more  difficult  to  make  a  short 
fibre  partake  of  the  nature  of  a  long  fibre  than  a  long  fibre 
that  of  a  short  fibre.  You  cannot  make  a  fibre  longer,  but 
you  can  always  make  it  shorter  by  beating.  A  fibre  that  has 
a  tendency  to  work  free  can  be  treated  in  such  a  way  as  to 
cause  it  to  work  wet.  Vice  versa ,  a  fibre  that  has  a  natural 
tendency  to  work  wet  can  be  so  treated  as  to  cause  it  to  work 
comparatively  free.  A  long  fibre  can  also  be  so  treated  as  to 
possess  some  of  the  characteristics  of  a  short  fibre.  It  may  be 
flattened  by  the  action  of  the  beater-roll  or  bruised  or  cut  sharply. 

It  has  been  above-stated  that  amorphous  cellulose  fibres,  when 
subjected  to  high  pressure  for  the  removal  of  water,  are  toughened 
and  do  not  exhibit  the  same  affinity  for  water  as  when  the 
same  are  dried  by  heat. 

When  papers  are  calendered  they  lose  some  weight,  which,  . 
1  believe,  is  generally  acknowledged  not  to  be  restored  on 
exposure  to  air.  It  appears,  therefore,  that  pressure  is  responsible 
for  this  by  bringing  the  particles  more  closely  into  contact.  A 
film  of  amorphous  cellulose  differs  from  a  sheet  of  paper,  in  that 
the  former  is  homogeneous  in  structure,  whilst  the  latter  is 
composed  of  a  mass  or  network  of  fibres.  It  does  not  follow  that 
pressure  will  add  to  the  strength  of  paper,  as  when  carried  to 
excess  it  may  so  affect  the  fibres  as  to  reduce  their  felting  power. 
In  this  respect,  then,  the  two  appear  to  differ. 

If  rigidity  is  obtained  by  the  removal  of  water  by  heat, 
it  results  often  in  the  production  of  a  more  or  less  brittle  paper. 

Hygroscopic  moisture  is  that  moisture  that  a  fibre  retains 
when  allowed  to  dry  in  an  ordinary  atmosphere.  When  wood 
retains  10  per  cent.,  cotton  and  linen  will  be  found  to  retain 
about  7  per  cent.  The  figures  in  a  measure  represent,  we  believe, 
other  things  being  equal,  the  relative  flexibilities  of  these  fibres 


Ill 


and  their  relative  powers  of  shrinkage ;  but  this  wants  further 
confirmation,  as  there  is  by  no  means  sufficient  data  to  go  upon. 

The  chief  function  of  water  in  the  production  of  a  sheet  of 
paper  is  to  render  the  fibres  which  are  suspended  in  it  as  a  medium 
flexible  and  expanded.  By  the  gradual  removal  of  water, 
which  results  in  the  production  of  inflexible  fibres,  we  see 
that  the  paper  is  formed. 

The  subordinate  function  of  water  is  to  provide  a  medium  in 
which  the  fibres  are  first  of  all  unravelled  and  often  disintegrated. 
The  medium  also  enables  the  fibres  to  be  held  in  suspension  and 
introduced  in  a  suitable  form  to  the  wire  of  the  paper  machine. 
This  suspension  of  the  fibres  also  allows  of  the  free  action  of  the 
shake  of  the  machine,  which  causes  the  fibres  to  interlace  and  build 
up  one  upon  the  other. 

The  first  action  is  primary,  and  the  second  entirely 
subordinate  ;  as  no  other  fluid  would  so  act  on  the  cellulose  as 
to  render  it  flexible  and  capable  of  felting,  no  other  liquid  medium 
could  be  made  to  answer  the  purpose. 

"We  have  seen  how  this  action  of  water  upon  cellulose  throws 
light  upon  the  working  of  various  fibres  on  the  machine,  and  the 
behaviour  of  paper  under  the  influence  of  moisture.  We  have 
seen,  also,  how  the  abstraction  of  moisture  affects  the  properties 
of  paper,  and  how  the  affinity  of  paper  for  water  on  immersion 
may  be  explained.  It  affords  also  an  explanation  of  what  is 
known  as  working  “  free  ”  or  working  “  wet,”  and  of  the  changes 
of  beaten  stuff  in  this  respect  after  long  keeping.  It  appears  to 
point  to  the  possibility  of  largely  modifying  the  physical 
properties  of  any  one  class  of  fibre  to  produce  a  range  of  papers 
that  could  be  only  otherwise  produced  by  using  different  raw 
materials.  It  appears  pi’obable,  also,  when  supplies  run  short,  or 
for  other  economic  reasons,  that  one  class  of  fibres  may,  within 
certain  limits,  be  supplied  by  another.  Much  is  already  being 
done  in  this  direction,  and  the  same  has  been  aided  largely  by 
improvements  in  the  art  of  beating  and  in  chemical  treatment. 
In  my  humble  opinion,  one  great  problem  of  the  future  will  be,  not 
the  discovery  or  the  utilisation  of  special  fibrous  raw  materials  for 
the  production  of  papers  for  which  they  are  considered  specially 
adapted,  but,  given  certain  cheap  and  abundant  supplies  of  raw 
material,  how  best  to  treat  and  modify  the  material,  both 
mechanically  and  chemically,  so  as  to  adapt  it  to  as  many  classes 
as  possible.  The  processes  must  be  both  cheap  and  effective,  and 
no  great  progress  can  be  expected  without  the  aid  of  the  strictest 
scientific  methods.  The  physical  properties  of  the  material  should 


112 


be  carefully  studied,  because,  after  all,  the  difference  between  one 
paper  and  another  is  chiefly  a  physical  difference,  which  can  be 
largely  wrought  by  mechanical  means.  I  think  it  must  be 
admitted  that  one  great  study  in  this  connection  is  that  of  the 
behaviour  of  cellulose  towards  water,  which  has  such  a  powerful 
modifying  effect  upon  its  physical  properties.  The  action  that 
water  has  upon  cellulose  is  largely  influenced  by  the  mechanical 
treatment  that  the  cellulose  receives  when  in  contact  with  water. 

It  appears,  therefore,  that  the  problems  of  the  future  will  be 
as  much  mechanical  as  chemical,  and  that  we  must  accept  the 
inevitable  by  abandoning  one  class  of  raw  material  in  favour  of 
a  cheaper,  if  it  is  by  mechanical  or  chemical  means  capable  of 
replacing  the  same  and  fulfilling  a  like  purpose. 


References. — The  foregoing  lecture  is  largely  abstracted  from  a  series  of  articles 
upon  “The  Function  of  Water  in  the  Formation  of  a  Web  of  Paper,”  scattered  over  several 
numbers  of  the  Paper-Maker,  but  now  out  of  print.  For  a  more  scientific  explanation  of 
t)ie  hydration  of  cellulose  see  the  various  publications  of  Cross  and  Bevan,  also  my  own 
communications  to  the  Chemical  News  and  the  Journal  of  the  Franklin  Institute. 


LECTURE  IX. 


*THE  PERMANENCE  OF  PAPER. 

The  permanence  of  paper — The  cause  of  deterioration— Early  attempts  at 
preservation — The  effects  of  the  fibre — Sizing— Clay — The  atmosphere — 
Sunshine — Temperature  and  moisture — Discoloration — Fading  of  water 
colours  —  Organisms  —  Moisture  —  Fermentation  —  N itrogenous  matter  — 
Methods  of  examination  for — Liability  to  decay. 


Theke  are  two  sets  of  causes  to  which  the  destruction  of 
papers  are  chiefly  due:  destruction  by  minute  organisms  and 
insects,  and  destruction  by  deterioration,  due  chiefly  to  oxidation. 
The  former  may  be  considered  as  purely  physiological  and  the 
latter  as  purely  chemical.  The  public  of  the  present  day  care 
little  about  the  permanence  of  a  paper  :  in  fact,  there  is  no 
reason  for  them  to  care,  as  far  as  the  greater  part  of  our  literature 
is  concerned.  With  the  ancients  it  was  quite  different  :  their 
paper  was  exceedingly  costly,  and  was  frequently  used  for  the 
preservation  of  valuable  records  that  were  kept  for  centuries 
without  destruction.  They  made  a  close  study  of  the  permanence 
of  papers. 

According  to  Pliny,  they  used  to  preserve  their  paper  and 
books  from  moths  by  washing  them  over  with  cedar  or  citron  oil. 
The  oil  gave  to  the  books  an  agreeable  scent,  and  they  were 
known  as  libri  cedrati.  Pliny  attributes  the  preservation  of  the 
books  found  in  the  grave  of  Numa  solely  to  this  precaution. 
He  states  that  a  certain  writer  named  Terentius,  when  digging  a 
piece  of  land  on  Mount  Janiculum,  found  in  a  stone  box  the 
book  of  Numa,  written  on  Egyptian  paper  (papyrus),  which  was 
quite  preserved,  in.  spite  of  the  fact  that  it  had  been  buried  350 
years  in  the  earth,  because  it  had  been  steeped  in  oil  of  cedar. 
Koops  says  that  there  were  found,  according  to  Count  Cavlus, 
sometimes  in  the  boxes  containing  Egyptian  mummies,  very  neat 


*  The  first  portion  of  this  lecture,  dealing  with  the  early  methods  of  preserving 
papers,  was  communicated  in  substance  to  the  columns  of  Paper  and  Pulp,  but  now  out 
of  print. 


114 


characters  written  on  linen.  Koops  imagines  that  the  linen  must 
have  been  dipped  in  size  or  gum,  or  the  ink  w'ould  have  blotted. 
I  mention  this,  as  I  believe  that  the  early  use  of  size,  or  something 
which  the  size  contained,  played  an  important  part  in  the 
preservation  of  papers,  and  fabrics  which  were  once  made  to 
answer  the  requirements  of  paper.  In  consequence  of  the  liability 
of  linen  to  become  mouldy,  skins  were  used  as  a  writing  material. 

The  Eoyal  Society  of  Sciences,  at  Gottingen,  in  1773,  offered 
a  premium  to  anybody  who  could  answer  the  following  questions  : 
How  many  insects  are  found  that  are  detrimental  to  records  and 
books?  Which  of  the  materials,  as  pap,  glue,  leather,  wood, 
thread,  paper,  &c.,  are  attacked  by  each  kind  ?  And  which  is  the 
best  and  most  approved  remedy,  either  to  preserve  records  and 
books  against  insects,  or  to  destroy  the  iosects  ?  Dr.  Herman, 
of  Strasburg,  obtained  the  premium. 

There  were  five  insects  that  were  proven  to  be  truly 
destructive.  There  were  nine  insects  that  are  generally  credited 
with  doing  harm  that  were  proved  to  be  without  mischief. 
There  were  six  that  appeared  doubtful;  among  them  may  be 
mentioned  the  book-louse  or  paper-louse.  To  preserve  the  books 
against  insects  and  to  destroy  the  latter,  there  were  many  recom¬ 
mendations.  Among  the  most  important  of  them,  as  far  as  we 
are  concerned,  is  to  recommend  the  bookbinder  to  use  glue  mixed 
with  alum  in  place  of  paste. 

Koops  tells  us  that  the  paper  of  his  time  in  North  America 
was  speedily  destroyed  by  dampness  and  insects.  In  consequence 
of  this,  Mr.  Francis,  of  Neufchatel,  induced  the  Society  of 
Sciences,  of  Philadephia,  in  1785,  to  offer  a  premium  for  the  best 
answer  on  the  following  question:  — 

Is  there  an  effectual  remedy  to  protect  paper  against  insects  ? 

The  Society  also  offered  another  premium  of  25  moidores  for 
the  best  method  of  making  paper  for  St.  Domingo  which  would 
resist  insects,  and  requested  to  have  samples  to  prove  its  quality. 
Several  answers  and  samples  were  received,  but  all,  so  Koops  tells 
us,  recommended  to  mix  the  size  or  sizing  agent  with  sharp  and 
bitter  or  other  ingredients  which  might  kill  the  insects.  Among 
the  substances  mentioned  we  find  vinegar,  alum,  vitriol,  salt, 
turpentine,  extract  of  aloes,  tobacco,  wormwood,  camphor,  and 
arsenic.  The  use  of  vitriol  would,  undoubtedly,  be  absurd,  on 
account  of  its  action  upon  the  paper.  Arsenic  is  a  good 
germicide,  but  might  be  found  objectionable  on  account  of  its 
poisonous  character.  The  one  substance  that  appears  to  have 
been  used  from  the  earliest  ages  up  to  the  present  time  is  alum. 


115 


Alum  at  the  present  time  is  found  to  be  a  very  necessary  ingredient 
of  paper,  but  its  powers  of  preservation  have  been  in  a  large 
measure  lost  sight  of. 

Koops  tells  us  “to  prepare  paper  for  preservation  against 
insects,  is  likewise  an  object  to  which  some  of  the  proprietors  of 
the  new  manufactory  now  building  at  Millbank  have  paid 
particular  attention;  and  they  flatter  themselves  they  will  likewise 
be  able  to  bring  to  sale,  and  to  lay  before  the  examination  of 
scientific  men  and  the  public  at  large,  paper,  in  this  view  much 
superior  to  any  heretofore  manufactured.” 

It  is  a  great  pity  that  these  questions  have,  since  the 
beginning  of  the  last  century,  been  almost  entirely  neglected. 

It  is  only  within  the  last  few  years  that  Germany  has, 
through  its  Government  Testing  Station  at  Berlin,  shown  to  the 
world  the  importance  of  looking  more  to  the  future.  The  public 
are  now  slowly  beginning  to  consider  whether  a  paper  has 
durability  or  not.  Public  opinion  seems  to  have  retrograded  since 
the  introduction  of  cheap  paper,  and  is  at  last  making  an  effort 
to  reconsider  those  questions  to  which  so  much  careful  attention 
was  paid  during  the  latter  half  of  the  eighteenth  century. 

In  this  lecture  we  are  considering  the  permanence,  or  rather 
the  want  of  permanence,  in  papers,  largely  from  the  point  of  view 
of  destruction  by  living  organisms,  but  with  the  assistance  of 
outside  agencies.  It  is  necessary  that  we  should  fully  appreciate 
the  conditions  under  which  organisms  are  capable  of  flourishing 
and  exercising  destructive  influences  upon  paper. 

Durability  of  paper  is  dependent  upon  many  factors.  These 
might  conveniently  be  summed  up  as  follows  : — 

A.  The  paper  itself. 

B.  The  atmosphere. 

C.  The  sunshine. 

D.  The  temperature  and  moisture. 

Under  A  we  have  (1)  Fibre. 

(2)  Sizing  material. 

(3)  Clay. 

Under  B  we  have  the  question  of  oxidation  brought  about  by  free 
exposure  to  the  air.  This  is  most  intense  when  the  sheets  are 
fully  exposed  and  hung  up,  and  the  liability  to  destruction  is 
greatest  in  an  atmosphere  such  as  that  of  London,  where  the 
impurities  from  combustion,  &c.,  exercise  a  destructive  influence. 

The  action  is  very  much  reduced  when  the  paper  is  stored  in 
the  form  of  reams,  or  when  it  is  contained  in  libraries,  &c.,  where 
the  air  can  get  at  it  very  little,  but,  nevertheless,  paper  even  in 


116 


the  leaves  of  books  shut  up  in  libraries  is  perpetually  in  contact 
with  air,  although  the  air  has  not  free  access.  Under  such 
conditions  the  action  of  the  air  is  reduced  to  a  minimum,  and  the 
action  of  light  or  sunshine  is  practically  nil,  except  on  the  edges, 
and  to  a  distance  of  about  one  inch  inwards. 

Paper  is  less  acted  upon  in  air  when  it  is  used  for  purposes  of 
illustration  and  covered  over  with  glass.  Under  such  conditions 
the  light  which  gets  to  it  has  a  greater  influence  than  the  air. 

As  regards  C,  the  sunshine  has  little  or  no  effect  when  the 
paper  is  stored  away.  Under  sunshine  we  would  include  any 
light  other  than  artificial  illumination,  as  all  the  light  which 
reaches  us  emanates  from  the  sun.  There  is  a  certain  amount  of 
action  even  in  an  ordinary  room  when  diffused  light  alone  is 
allowed  to  enter,  but  the  effect  of  light  is  much  intensified  when 
the  paper  is  exposed  directly  to  sunshine,  especially  in  summer 
time,  no  matter  whether  the  sunlight  traverses  a  glass  window 
or  not.  Paper  such  as  common  “  news,”  if  left  in  the  sun  for 
some  days,  will  have  become  discoloured,  and  will  in  fact  have 
undergone  as  much  change  as  a  paper  would  if  left  in  a  dark  place 
for  one  year.  Qua  light,  artificial  lights  such  as  gas,  candle  light, 
and  electric  light  have  much  less  effect  than  sunlight,  either 
direct  or  diffused,  but,  of  course,  gas  is  highly  objectionable 
where  permanent  records  are  stored,  on  account  of  the  products 
of  combustion  being  destructive.  It  should  be  remembered,  that 
the  kind  of  light  which  destroys  papei’s  is  just  that  kind  which 
must  affect  a  photographic  plate,  and  consequently  those  sources 
of  light  are  the  most  active  which  contain  the  greatest  amount 
of  actinic  or  chemical  rays.  Sunlight  is  far  more  active  than  the 
rest  for  this  very  reason. 

The  question  of  fading  is  distinct  from,  although  closely 
allied  to,  the  question  of  deterioration  of  paper.  I  would  define 
fading  as  being  a  change,  not  in  the  paper  itself,  but  in  the 
material  used  to  colour  the  paper.  As  the  fading  of  a  paper  may 
result  in  a  deterioration,  at  any  rate,  from  a  commercial  point  of 
view,  the  question  may  very  well  be  considered  here.  As  far  as  I 
am  aware,  there  is  no  publication  presented  to  the  paper  trade 
dealing  with  this  aspect  of  the  subject,  but.  nevertheless,  it  has 
been  most  carefully  investigated  from  the  point  of  view  of  the 
permanency  of  colours  used  for  water-colour  drawings.  Such 
work,  however,  does  not  cover  the  whole  of  the  ground,  because 
water-colours  are  only  superficially  applied  to  the  paper  after 
manufacture,  whex-eas  ordinary  papers  are  coloured  in  the  course 


117 


of  manufacture,  and  the  colour,  whether  pigment  or  dye,  is  dissem¬ 
inated  through  the  body  of  the  paper.  Moreover,  there  is  another 
distinction — water  colours  are  only  used  on  papers  of  a  particular 
class,  and  prepared  especially  for  the  purpose — i.e.  drawing  papers; 
whereas  most  tinted  and  coloured  papers,  especially  those  of  very 
pronounced  and  brilliant  colours,  are  generally  made  of  common 
and  cheap  materials.  In  our  consideration  of  this  matter  we  will 
exclude  enamelled  papers. 

The  researches  conducted  by  Captain  Abney  and  Dr.  Russell 
throw  light  on  the  whole  subject,  and  their  conclusions  should 
prove  instructive  to  paper  makers  and  stationers,  as  the  conditions 
which  affect  the  fading  of  water  colours  apply  also,  and  in  a  like 
degree,  to  the  fading  of  tinted  papers,  and  it  will  readily  be  seen 
that  the  kind  of  light  which  is  most  destructive  and  the 
conditions  which  give  rise  to  the  most  rapid  discharge  of  colour 
are  such  as  also  affect  the  fibre  to  the  greatest  extent.  It 
therefore  very  often  happens  that  when  a  tinted  paper  fades,  not 
only  is  the  colour  discharged,  but  the  fibre  is  at  the  same  time 
disintegrated,  discoloured,  and  destroyed,  and  the  paper  instead  of 
merely  losing  its  colour  and  showing  a  white  background, 
especially  in  the  case  of  mechanical  wood,  gives  rise,  when  acted 
upon,  to  a  brown  and  dirty  coloration. 

*  “  But  another  point,  and  a  very  important  point  for  the 
critics  to  take  hold  of,  is  this.  It  is  all  very  well  to  say  that 
light  alone  causes  fading,  but  how  about  light  and  heat  together  ? 
Would  not  the  heat  aid  the  light?  This  possible  criticism  was 
combated,  I  hope,  in  a ,  successful  way.  A  certain  series  of 
pigments,  washed  on  paper,  were  taken  and  exposed  on  a  vessel 
containing  boiling  water ;  similar  papers  were  exposed  to  the 
sunlight  free,  that  is  to  say,  without  the  presence  of  boiling  water. 
In  some  cases  the  fading  was  rather  more  rapid,  in  others  less, 
and  you  will  readily  see  why  in  some  cases  it  was  rather  less  rapid. 
You  require  moisture  }jlus  air  in  order  to  cause  fading,  and  if  you 
heat  paper,  of  course  you  take  away  part  of  the  moisture,  one  of 
the  agencies  which  are  conducive  to  fading.  But  the  difference 
between  those  exposed  on  boiling  water  and  those  exposed 
without  was  so  small  that  you  might  take  the  action  of  light  plus 
heat  as  equivalent  to  the  action  of  light  alone.” 

We  must  conclude,  therefore,  from  this  series,  that  heat  does 
not  promote  or  accelerate  the  fading  of  colours  in  paper.  In 


*  Tlie  above  quotations  are  from  Cantor  Lectures  before  the  Society  of  Arts  on  Light 
and  Colour,  delivered  in  1888,  by  Captain  Abney,  F.R.S. 


118 


order  to  ascertain  what  kind  of  light  had  the  most  effect,  the 
authors  exposed  papers  coated  with  different  pigments  under 
coloured  glasses,  so  as  to  shut  off  different  portions  of  light.  It 
was  found  that  under  the  red  and  green  glasses  the  fading  of  the 
few  pigments  that  succumbed  was  so  small  that  it  required  a 
practised  eye  to  distinguish  it.  but  under  blue  glass  the  fading 
was  almost  identical  with  the  fading  under  white  glass.  Now 
the  red  waves  of  light  are  the  longest  and  the  blue  waves  are  the 
shortest,  therefore  it  is  the  waves  of  light  of  the  quickest  oscilla¬ 
tion  which  bring  about  the  fading.  It  was  furthermore  found 
that  every  pigment  (with  a  few  exceptions  which  we  need  not 
trouble  ourselves  about)  is  permanent  when  exposed  to  light  in 
vacuo.  This  indicates  that  light  alone  without  the  presence  of 
air  and  moisture  will  not  fade  papers.  It  was  furthermore  found, 
that  when  a  paper  is  tinted  with  two  colours  one  of  which  is  fast 
and  the  other  is  fugitive,  the  fugitive  colour  is  destroyed,  and  the 
fast  colour  is  left  unimpaired  by  exposure  to  light.  It  was 
established  that  moisture  and  oxygen  were  essential  for  the  fading 
of  colours  in  paper ;  the  question  remained  whether  they  would 
fade  without  light.  A  stream  of  oxygen  was  passed  through  a 
tube  containing  some  papers  coated  with  pigments.  Half  of  each 
paper  was  damped  and  the  other  half  left  dry.  When  this  was 
connected  with  an  ozone  generator,  “  a  great  many  are  bleached 
entirely,  thus  proving,  if  you  have  ozone  and  moisture  together, 
you  get  a  bleaching  without  the  presence  of  light  at  all.”  This 
action  is  very  rapid.  These  are  conditions  that  prevail  at  seaside 
places.  “We  come  then  to  the  conclusion  that  oxygen  and 
moisture  are  sufficient  for  the  fading  of  water-colour  pigments, 
and  that  it  is  not  absolutely  necessary  that  there  should  be  light 
present  in  order  that  this  fading  may  take  place.”  It  will  readily 
be  seen  that  the  conditions  here  favouring  the  fading  of  colours 
are  on  all  fours  with  the  conditions  which  are  found  to  bring 
about  the  destruction  of  the  fibre  itself.  Erfurt’s  book  on  the 
dyeing  of  paper  pulp  does  not  deal  with  this  aspect  of  the  subject. 

Then  apart  from  the  above,  we  have  the  question  D  or 
temperature  and  moisture.  As  previously  explained,  when  paper 
contains  sizing  material  in  a  moist  atmosphere  and  within  certain 
limits  of  temperature,  the  deterioration  or  destruction  of  the 
sizing  material  is  extremely  rapid.  If,  however,  the  temperature 
is  fairly  high,  i.e.,  high  enough  to  prevent  the  growth  of 
organisms,  the  deterioration  of  the  paper  itself  would  not  be  so 
rapid,  although  the  gelatine  size  would  undoubtedly  be  destroyed. 

When  paper  is  totally  immersed  in  water  the  fibres  are  not 


119 


so  liable  to  decay  as  when  the  paper  is  hung  up  or  exposed  to  the 
atmosphere  charged  with  moisture.  These  various  details  will  be 
considered  more  particularly  further  on. 

There  are  other  conditions  which  will  affect  the  permanence 
of  papers.  We  can  take  an  extreme  case  such  as  ordinary  soil. 
Even  a  pure  cellulose  paper  when  buried  in  the  ground  or  covered 
over  with  ordinary  earth  will  be  completely  disintegrated,  and 
even  dissolve  away  in  a  very  short  period  of  time,  due  to  the 
“  humic  ”  and  “  ulmic  ”  substances  contained  in  the  soil,  which 
have  a  rapid  solvent  effect  even  upon  pure  cellulose. 

We  will  now  consider  paper  as  a  medium  for  the  cultivation 
and  growth  of  bacteria  and  minute  organisms,  because  by  so  doing 
we  shall  be  better  able  to  form  a  mental  grasp  of  the  conditions 
which  favour  the  growth  of  these  organisms,  in  the  course  of 
which  they  bring  about  the  destruction  of  the  paper. 

It  may  be  taken  generally  that  any  organism  which  is 
capable  of  development  or  cultivation  on  gelatine  is  also  capable 
of  development  on  all  papers  that  contain  animal  size.  Further¬ 
more,  all  those  oi’ganisms,  moulds,  yeasts,  &c.,  which  are  capable 
of  developing  and  acting  on  starch  in  one  or  other  of  its  forms, 
are  also  capable  of  developing  and  growing  in  papers  which  have 
been  sized  with  starch,  provided,  of  course,  that  such  papers  are 
exposed  under  such  conditions  as  will  favour  the  growth  of  these 
organisms.  Rosin  size,  however,  is  not  affected  by  organisms,  but 
on  the  other  hand  it  is  the  most  susceptible  of  all  the  sizing 
materials  to  the  action  of  light. 

Some  years  ago  I  made  use  of  a  process  called  the  “  fermen¬ 
tation  process,”  which  was  used  for  the  destruction  of  gelatine 
and  starch,  and  other  sizing  materials  used  in  papers,  before  the 
papers  were  reduced  to  pulp.  The  process  was  an  extremely 
simple  one.  Papers  were  taken  in  bags  or  bales  and  immersed 
in  water  for  a  few  minutes  so  as  to  thoroughly  wet  them  through. 
These  bales  were  then  placed  in  a  damp  place,  not  too  cold  or 
too  hot,  and  allowed  to  remain  in  the  bales  in  a  damp  condition, 
or  placed  in  tubs,  and  were  kept  away  from  exposure  to  the 
atmosphere  and  in  the  dark.  After  a  time  a  change  took  place 
in  the  appearance  of  the  papers.  They  developed  a  musty  smell. 
They  also  developed  brilliant  spots,  red  and  blue  and  different 
colours,  showing  the  formation  and  development  of  organisms 
producing  pigments. 

These  organisms  preyed  upon  the  sizing  material  and 
destroyed  it,  some  of  them  converting  the  size  into  colouring 
matter,  whilst  other  organisms  known  as  the  liquefying  organisms, 


120 


broke  down  the  gelatine  and  destroyed  its  gelatinising  properties 
altogether  and  rendered  it  soluble. 

After  this  treatment  had  been  allowed  to  develop  to  the 
extent  of  destroying  the  sizing  material,  and  before  it  had  any 
chance  of  acting  on  the  cellulose  itself,  the  papers  were  pulped  in 
the  usual  way,  and  the  fermentation  process  could  be  arrested 
entirely  in  the  process  of  pulping  by  the  addition  of  a  small 
quantity  of  antiseptic,  which  entirely  destroyed  the  organism. 

It  may  interest  you  to  know  what  the  organisms  are  which 
are  capable  of  acting  in  this  way  upon  the  nitrogenous  and 
farinaceous  matters  contained  in  papers.  I  will  give  you  some 
idea  of  a  few  of  them : — 

There  is  Saccliaromyces  nigia ,  which  forms  a  black  crust  on 
the  surface  of  gelatine. 

The  Bacterium  indicum  produces  a  brilliant  red  coloration. 

There  is  Saccliaromyces  rosaceous,  which  produces  a  pink 
colour. 

On  certain  forms  of  starch  the  Bacterium  prodigiosum 
produces  a  cloudy  red  growth,  which  gradually  acquires  a 
brownish  colour,  and  in  doing  so  it  breaks  down  the  starch. 

A  very  common  form  of  mould,  the  Penicillium  glaucum, 
produces  a  greyish  spot  on  the  surface  of  starch. 

Mr.  C.  !F.  Cross,  in  his  article  on  “Paper  and  Paper 
Standards,”  which  originally  appeared  in  Science  Progress,  drew 
attention  to  this  matter.  He  gives  an  easy  and  simple  way  of 
arriving  at  the  relative  durabilities  of  different  papers  by  a  few 
simple  experiments,  which  I  give  in  his  own  words : — 

“1.  Place  the  specimens  each  in  a  stoppered  bottle 
containing  a  few  c.c.  of  water.  Set  aside  in  a  ‘  warm  corner,’ 
and  after  10  or  14  days  note  what  has  happened.  Papers  of 
Class  L*  will  have  proved  themselves  an  excellent  nidus  for 
micro-organisms  of  all  types.  Colonies  of  these  will  have 
established  themselves  after  their  manner,  and  gorgeous  effects 
in  crimson,  yellow7,  and  blue  will  reward  the  observer.  The 
filter  paper  (which  by  the  way  must  not  be  allowed  to  come  in 
actual  contact  with  the  water)  will  not  show  any  such  effects. 
They  are  obviously  due  to  the  nitrogenous  colloid,  the  gelatine 
used  in  sizing  the  paper,  for,  as  regards  the  cellulose  fibres  of 
which  they  are  composed,  the  two  papers  may  be  considered  as 
identical.  Probably  also  the  papers  of  Classes  II.+  and  IH.j 


*  Class  I. — Ray  papers. 

+  Class  II. — Chemical  wood. 

j  Class  III. — Mixtures  containing  mechanical  wood. 


121 


will  not  have  grown  any  organisms.  In  other  words,  the  pure 
celluloses  are  not  susceptible  to  the  direct  attack  of  organisms. 
But,  given  a  supply  of  the  necessary  nitrogenous  and  saline 
nutriments,  they  yield  more  or  less  readily  in  the  inverse  order 
of  our  classification.  They  yield,  by  undergoing  hydrolysis,  to 
soluble  products  allied  to  tbe  starch  sugar  series,  capable  of 
assimilation  by  living  organisms.  The  celluloses  of  the  cereals 
and  of  esparto  are  very  readily  so  attacked,  and  for  this  reason 
the  tissue  constituents  of  the  straws  are  considerably  digested 
in  their  passage  through  the  digestive  tract  of  the  herbivora. 
Precisely  for  this  reason  the  celluloses  of  straw  or  esparto  rank 
very  much  below  the  normal  or  typical  cotton  cellulose  as  paper¬ 
making  materials.  The  wood  celluloses  are  intermediate.” 

The  plan  of  suspending  strips  of  paper  of  known  composition 
in  a  stoppered  bottle  with  water  at  the  bottom  but  out  of  direct 
contact  with  the  paper  is  very  easy  and  very  instructive.  All 
paper  may  be  said  to  contain  the  germs  of  putrefaction  in  a 
latent  state,  and  the  air  is  always  teeming  with  them.  When 
paper  is  brought  into  an  atmosphere  of  this  kind,  and  provided 
it  contains  sizing  material  upon  which  the  organisms  can  start 
their  growth,  a  change  soon  takes  place.  This  test  is  a 
thoroughly  practical  one,  and  helps  us  to  distinguish  between 
different  papers  and  their  relative  liability  to  mouldiness  in  such 
climates  as  prevail  in  parts  of  India  and  South  America. 

It  may  readily  be  seen  that  this  subject  is  an  important  one 
to  the  stationer  as  well  as  the  papermaker,  as  he  should  certainly 
know  under  what  conditions  papers  are  liable  to  destruction  by 
organisms  and  other  agencies. 

It  happens  sometimes  that  papers  are  used  under  conditions 
which  would  give  rise  to  the  growth  and  development  of  these 
organisms,  and  under  such  circumstances,  substances  should  be 
added  to  the  paper  in  the  form  of  antiseptics  to  prevent  such 
growth  if  possible,  but,  better  still  where  practicable,  an  attempt 
should  be  made  to  use  papers  which  do  not  contain  sizing  material 
liable  to  putrefaction. 

As  regards  modern  means  of  applying  antiseptics  to  paper, 
this  subject  belongs  to  the  domains  of  the  bacteriologist  and  the 
chemist.  Thanks  to  the  brilliant  researches  of  some  of  our 
leading  scientists,  the  power  of  many  substances  to  arrest 
putrefaction  has  been  largely,  if  not  exhaustively,  investigated. 
As  many  of  these  substances  are,  if  not  carefully  applied,  not 
safe  to  handle,  I  should  hardly  like  to  prescribe  how  and  under 
what  conditions  such  substances  should  be  used,  although  I  have 


122  • 


had  considerable  experience  with  many  of  them.  Chemists  who 
have  studied  the  matter  can  prescribe  when  the  specific  require¬ 
ments  are  made  known.  There  are  many  different  treatments. 
For  instance,  we  may  want  to  treat  a  tub-sized  paper  so  that  it 
will  stand  the  Indian  climate,  or  we  may  want  to  go  further  and 
treat  a  paper  so  that  it  may  be  used  as  an  antiseptic  bandage,  and 
not  only  be  sterile  in  itself,  but  have  the  power  of  arresting  or 
destroying  the  perishable  matter  with  which  it  comes  in  contact. 
The  questions  naturally  arise  :  How  and  where  is  the  substance  to 
be  applied  to  the  paper  or  stuff?  What  stuff  and  ingredients 
should  be  used  ?  What  antiseptic  should  be  used,  and  in  what 
quantity  to  give  the  desired  result? 


LECTURE  X.  (Part  I.) 


SUNDRY  PHYSICAL  QUALITIES  OF  PAPER. 

The  Society  of  Arts  Committee — Their  decision — The  acid  action  of 
drawing  papers — Influence  of  rosin  and  gelatine  sizing  on  strength — 
Deterioration  due  to  mechanical  wood — The  lasting  qualities  of  other 
fibres— Composition  of  blottings — Effects  of  moisture  and  heat  upon 
expansion — Discoloration  of  papers  by  sunlight. 


The  chief  information  we  have  on  the  subject  of  deterioration 
is  contained  in  a  report  issued  by  the  committee  appointed  by  the 
Society  of  Arts  to  consider  the  question.  This  committee  made  a 
thorough  examination  of  various  papers  used  in  this  country  with 
a  view  to  adopting  certain  standards  of  quality  and  making  certain 
recommendations  not  only  to  papermakers  but  also  to  those  who 
are  responsible  for  the  uses  to  which  paper  is  put,  namely,  the 
stationers,  printers,  publishers,  the  learned  societies,  and  last  of  all, 
the  general  public.  In- passing  I  would  briefly  refer  to  the 
responsibility  that  rests  chiefly  with  the  publishers  and  printers 
of  literature  required  to  be  of  a  lasting  nature.  With  literature 
“  which  to-day  is  and  to-morrow  is  cast  into  the  oven  ”  there  is 
no  responsibility  beyond  the  exigencies  of  the  moment,  but  it  is 
important  if  not  essential  that  the  users  of  paper  especially  should 
know  something  of  the  transient  nature  of  our  modern  and  cheap 
papers ;  they  should  also  know  what  papers  will  last  and  under 
what  conditions  such  paper  will  stand  the  test  of  time.  The 
information  on  this  subject  is  at  present  very  incomplete,  but  I 
shall  do  what  little  I  can  to  give  information  bearing  on  this 
point  within  the  short  space  of  this  lecture  which  would  be  of 
service.  The  report  of  the  committee  of  the  Society  of  Arts  was 
published  in  1898,  and  since  that  date  other  facts  have  come  to 
light  which  might  have  modified  the  committee’s  opinion.  There 
are,  however,  various  points  which  deserve  our  serious  consideration, 
and  to  which  I  will  briefly  refer. 


124 


It  is  pointed  out  that  actual  disintegration  has  been  proved 
to  exist  in  papers  of  all  grades,  from  rag  papers  to  those  of  the 
lowest  quality,  but  it  is  a  question  not  only  of  material  but  also 
of  conditions  under  which  the  papers  are  exposed.  There  are 
certain  destructive  influences  at  work  apart  from  the  ordinary 
wear  and  tear. 

A  great  deal  of  the  damage  to  papers  is  the  result  of  exposure 
to  an  atmosphere  where  gas  is  used.  The  products  arising  from 
the  gas  give  off  sulphur,  first  of  all  in  the  form  of  sulphurous  acid, 
which  is  afterwards  oxidised  to  sulphuric  acid.  This,  in  contact 
with  the  paper,  may  bring  about  disintegration,  even  in  the  finest 
qualities.  Then  we  have  the  question  of  a  discoloration,  which 
takes  various  forms,  but  is  largely  due  to  contact  with  air  and 
exposure  to  light.  In  the  case  of  papers  containing  such 
products  as  mechanical  wood,  this  produces  oxidation,  and  results 
in  a  darkening,  especially  in  the  edges  of  a  book,  which  are 
more  exposed  to  the  atmosphere. 

In  all  papers  acid  bodies  appear  to  be  formed  as  a  result  of 
oxidation. 

The  committee  suggest  that  as  rosin  is  the  cause  of  the 
deterioration,  as  little  rosin  should  be  used  for  the  purpose 
of  printings  as  is  practicable,  and  that  it  should  not  exceed  2  per 
cent.  It  is  a  well-known  fact  that  bodies  of  the  nature  of  rosin,  if 
contained  in  large  quantities  in  a  paper,  will  bring  about  its 
disintegration,  even  if  the  fibres  consist  of  pure  cellulose.  This- is 
exemplified  particularly  in  paper  such  as  tracing  paper,  which 
contains  a  large  proportion  of  substances  of  a  resinous  nature. 

Then  the  question  of  what  is  known  as  acidity  is  an  important 
one.  It  is  a  question  whether  papers  may  be  finished  with  a 
slight  excess  of  alum,  which  gives  to  the  paper  an  acid  reaction 
with  litmus  but  is  neutral  to  methyl  orange. 

The  question  of  the  so-called  acidity  of  papers  came  to  the 
fore  when  Professor  Hartley  announced  to  the  Chemical  Society 
that  the  acid  reaction  of  litmus  in  Whatman’s  drawing  was  due 
to  the  presence  of  sulphuric  acid  as  a  residue  from  souring  in  the 
course  of  manufacture. 

After  this  I  studied  the  question  and  tested  these  drawing 
papers  most  carefully  with  different  indicators,  and  contributed 
a  paper  to  the  Chemical  Society,  showing  that  the  so-called  acidity 
of  these  papers  was  not  due  to  the  presence  of  free  acid  at  all,  but 
that  papers  such  as  Whatman's  gave,  necessarily,  a  red  coloration 
with  litmus,  that  this  red  coloration  is  not  the  result  of  free  acid. 


125 


as  proved  from  the  fact  that  the  papers  give  a  basic  reaction 
with  methyl  orange. 

I  have  already  treated  of  this  subject  at  some  length  in  a 
previous  lecture,  so  that  further  reference  is  not  needed  here. 

It  is  important  that  the  papers  should  not  contain  an 
appreciative  quantity  of  chlorides.  Some  chlorides  appear  to  be 
harmless,  but  others  are  liable  to  decomposition  and  do  a 
considerable  amount  of  harm.  The  committee  also  draw  attention 
to  the  question  of  colour.  There  is  great  danger  when  materials 
are  over-bleached,  as  the  bleaching  action  has  the  effect  of  rendering 
the  material  susceptible  to  change  by  atmospheric  influences. 
Eag  might  be  rendered  as  susceptible  to  atmospheric  influence  by 
bleaching  as  esparto  is  in  the  ordinary  course. 

After  careful  consideration,  the  committee  came  to  the 
conclusion  that  10  per  cent,  should  be  the  maximum  quantity 
of  mineral  used  in  papers  and  publications  that  are  required  for 
permanent  use. 

They  were,  no  doubt,  justified  in  this  recommendation,  which 
certainly  ought  to  be  acted  upon,  because  it  is  now  an 
acknowledged  fact  that  mineral  matter  in  excess  reduces  the  life 
of  papers. 

The  findings  of  the  committee  are  as  follows — First,  normal 
standard  of  quality  for  book  papers  required  for  publications  of 
permanent  value.  For  such  papers  they  would  specify  as  follows— 

Fibres.  Not  less  than  70  per  cent,  of  fibres  consisting  of 
cotton  flax  or  hemp.. 

Sizing.  Not  more  than  2  per  cent,  rosin,  and  finished  with 
the  normal  acidity  of  pure  alum  loading. 

Loading.  Not  more  than  10  per  cent,  total  mineral 
matter. 

After  the  committee’s  report  are  given  a  number  of  abstracts 
from  papers  bearing  on  the  subject  of  deterioration  and  allied 
subjects.  These  are  mostly  contributions  by  Herzberg.  I  will 
briefly  allude  to  one  or  two  of  the  more  important  conclusions, 
arrived  at,  which,  I  think,  in  the  main  will  be  of  interest  both  to 
papermakers  and  to  stationers. 

One  important  point  is  the  influence  of  gelatine  sizing  on  the 
strength  of  papers.  A  number  of  papers  consisting  of  linen, 
hemp,  and  cotton  fibres  with  1.5  per  cent,  of  rosin  sizing  were 
coated  with  one,  two,  and  three  coats  of  gelatine  respectively. 
The  results  show  that  the  breaking  length  and  elasticity  w'ere 
noticeably  increased  by  repeated  sizing. 


126 


la  a  further  series  it  was  found  that  the  breaking  strain  was 
increased  by  successive  sizing  up  to  four  treatments.  Beyond  this 
number  it  remained  slightly  below  its  maximum.  The  paper  at 
the  fourth  treatment  with  size  was  1.7  times  the  strength  of  the 
unsized  paper.  The  elasticity  reached  the  maximum  of  1.39 
times  the  elasticity  of  the  unsized  paper  with  the  first  sizing. 

Of  course,  one  must  not  draw  the  inference  from  this  that 
paper  tub-sized  in  the  web  gains  in  strength  to  the  same  extent, 
nor  is  it  conclusive  that  all  the  additional  strength  is  due  to  the 
gelatine.  Much  wetting  with  water  alone  repeatedly  and  loft¬ 
drying  would  tend  to  improve  the  strength  of  a  paper. 

The  same  water-leaf  paper  was  also  treated  with  size  and 
starch  ancl  the  results  shown  were  very  similar  to  those  shown 
with  the  gelatine-sized  paper.  It  seems  fairly  conclusive,  there¬ 
fore,  that  all  papers  are  increased  in  strength  as  well  as  in  their 
elasticity  by  tub-sizing,  and  I  think  this  is  a  general  experience 
of  the  practical  papermakers.  The  starch  trials  have  not  much 
practical  value,  as  starch  is  applied  not  to  the  web  but  to  the  pulp. 

With  rosin  sizing,  on  the  other  hand,  the  results  obtained 
by  Martens  show  a  very  different  result.  They  all  show  a  lower 
breaking  strain  than  the  papers  of  similar  composition,  but 
without  the  rosin.  It  is  concluded,  therefore,  that  rosin  sizing 
diminishes  the  strength  and  elasticity  of  mechanical  wood  papers. 
I  believe  that  Hoffman,  in  his  treatise  on  papermaking,  also  makes 
the  same  statement. 

In  order  to  test  this  treatment  I  made  a  series  of  tests 
with  mechanical  wood  containing  different  portions  of  rosin,  and 
instead  of  basing  my  conclusions  on  one  or  two  samples, 
I  prepared  30  or  40  mixtures  and  carefully  tested  them  all,  and 
compared  them  with  a  number  of  mixtures  made  without  the 
addition  of  any  rosin  size.  These  results  were  published  in  the 
Paper-Maker.  It  is  needless  to  refer  to  them  in  detail,  but  at 
first  sight  they  do  not  appear  to  confirm  the  results,  or  rather  the 
conclusions,  of  other  observers.  But  I  was  working  on  paper 
containing  100  per  cent,  of  mechanical  wood.  I  think  it  is  not 
difficult  to  explain  the  difference  in  the  two  sets  of  results.  If  the 
paper  is  very  weak,  rosin  is  capable  of  giving  it  additional 
strength,  and  the  additional  strength  that  rosin  can  give  is  partly 
dependent  upon  the  amount  used,  but,  unless  the  paper  is  very 
weak  the  rosin  has  no  power  of  adding  to  its  strength.  Martens’ 
statement  that  rosin  sizing  thus  diminishes  the  strength  and 
•elasticity  of  mechanical  wood  pulp  papers  requires  to  be  qualified. 
With  certain  papers,  as  for  instance  the  mixture  of  mechanical 


127 


wood  and  with  a  small  amount  of  sulphite,  the  rosin  may  exert 
no  influence,  either  one  way  or  the  other,  upon  the  strength,  but 
if  the  stock  is  further  strengthened  by  the  addition  of  more 
sulphite,  the  rosin  is  found  to  have  a  retarding  effect  upon  the 
strength.  Martens’  statement  that  a  certain  paper  when  sized 
with  gelatine  shows  a  marked  increase  in  strength  with  increased 
percentage  of  mechanical  wood,  but  the  elasticity  diminishes, 
rather  confirms  my  view  that  both  rosin  and  gelatine  have 
strength-giving  qualities.  Gelatine,  being  much  the  stronger  of 
the  two,  would  exert  a  much  greater  influence  on  mechanical  wood 
paper  than  rosin  would. 

It  becomes,  therefore,  a  question  of  the  relative  strength  or 
strength-giving  qualities  of  the  fibres  of  which  paper  is  composed 
and  of  the  sizing  material. 

It  comes  to  this,  therefore,  that  the  strength  of  the  paper  is 
the  mean  strength  of  its  ingredients.  If  you  add  gelatine  to 
the  paper  and  the  strength-giving  qualities  of  the  gelatine  are 
greater  than  that  of  the  fibres  of  which  it  is  composed,  the 
ultimate  strength  of  the  sized  paper  will  be  somewhat  greater 
than  the  waterleaf.  If  the  waterleaf  is  composed  of  material 
which  is  very  weak  in  the  first  instance,  it  is  natural  that  the 
effect  of  gelatine  should  have  an  enormous  increase  upon  its 
strength.  Eosin,  as  we  know,  has  much  less  strength-giving 
qualities  than  gelatine,  and  consequently  when  rosin  is  added  to 
size  papers  composed  almost  wholly  of  mechanical  wood,  there 
is  only  a  slight  increase  in  strength,  but  when  the  furnish  contains 
more  sulphite  fibre  there  is  a  slight  diminution  in  strength  with 
rosin,  although  an  increase  with  gelatine.  This  explains  the 
apparent  contradiction  between  my  own  and  Herzberg’s  conclu¬ 
sions.  I  do  not  wish  to  doubt  his  figures,  only  his  general 
conclusions. 

Martens  gives  some  very  interesting  figures  with  reference 
to  the  effects  of  glazing  on  the  strength  of  papers.  His  figures 
show  that  there  is  an  increase  of  from  8  to  9  per  cent,  in  the 
strength  of  the  paper  after  glazing,  and  that  this  increase  takes 
place  in  a  similar  manner  whether  across  or  in  the  direction  of 
the  web.  and  that  there  is  very  little  difference  between  heavy 
and  light  glazed  papers  in  this  respect,  but  instead  of  an  increase 
of  elasticity  as  a  result  of  glazing,  there  is  an  actual  diminution  of 
from  8  to  11  per  cent.  This  is  what  one  might  expect  on  a  paper 
that  has  been  compacted  by  glazing. 

A  paper  which  bulks  fairly  well  should  have  a  greater 
elasticity  than  one  which  is  very  much  compressed.  He  does  not 


128 


state  what  kind  of  glazed  surface  he  used.  The  effect  of  plate 
glazing,  especially  when  the  material  has  been  crushed  by  over¬ 
pressure,  is  very  well  known  to  papermakers.  It  materially 
reduces  the  folding  qualities,  so  much  so  that  when  a  sheet  is 
sharply  folded  it  very  often  cracks.  This,  of  course,  must  be 
avoided,  especially  for  papers  manufactured  for  the  making  of 
envelopes.  This  is  generally  the  result  of  over-pressure  being 
applied  to  the  glazing  rolls,  or  the  passing  of  the  stack  too  many 
times  between  the  rolls. 

The  Society  of  Arts  committee  do  not  appear  to  have  drawn 
any  attention  to  the  effect  which  glazing  or  over-glazing  have  upon 
the  ink-bearing  qualities  of  the  papers.  Some  papers  are,  I 
believe,  often  very  much  lessened  in  their  ink-bearing  qualities 
after  glazing. 

Martens  states  that  in  discussing  the  durability  of  printing 
paper  in  the  present  day,  it  has  been  proved  that  the  daily  papers 
have  been  printed  on  paper  which  rapidly  becomes  yellow,  and 
he  attributes  this  to  the  use  of  mechanical  wood  pulp.  He 
furthermore  asserts  that  three  other  new  materials  used  in 
paper  manufacture — wood,  straw  cellulose,  and  esparto— are 
believed  to  possess  similarly  bad  characteristics,  but  states  that 
they  have  been  in  use  too  short  a  time  for  any  certainty  to  exist 
as  to  their  durability.  Anybody  who  has  had  the  experience 
with  straw  and  esparto  will  know  that  they  are  nothing  like  so 
perishable  as  mechanical  wood  pulp,  although  they  are  more 
perishable  than  chemical  wood  pulp. 

The  fact  is  that  they  are  practically  speaking  oxy-cellulose, 
and  behave  towards  atmospheric  influences  much  as  over-bleached 
cotton  pulp  would  do.  The  durability,  as  far  as  we  know,  might 
be  stated  as  follows : — Mechanical  wood  pulp,  straw,  esparto, 
chemical  wood  pulp,  linen,  cotton,  cceteris  paribus ,  mechanical 
wood  being  the  least  and  cotton  and  linen  the  most  durable. 

We  have  now  a  proof  that  chemical  wood  pulp,  if  carefully 
prepared,  is  a  material  not  far  short  in  durability  to  cotton  an 
linen,  but  no  paper  has  been  made  a  sufficient  length  of  time  for 
us  to  state  with  any  degree  of  certainty  how  chemical  wood  pulp 
will  stand  the  test  of  long  storage  and  use,  say  over  200  years. 

Herzberg’s  examination  of  papers  made  from  sulphide  cellulose 
showed  that  in  ten  months  the  paper  possessed  a  slightly  higher 
tearing  strength,  but  that  it  had  lost  considerably  in  elasticity. 
Martens  further  emphasises  the  fact  that  for  all  publications  of 
permanent  value  cotton  and  linen  fibres  alone  should  be  used. 


129 


Herzberg  gives  some  interesting  figures  in  regard  to  the 
strength  and  elasticity  of  samples  taken  from  different  parts  of  the 
same  sheet.  He  shows  that  there  is  specially  a  variation  in  the 
case  of  paper  made  with  long  fibres,  and  with  heavily  loaded 
papers,  but  all  the  variations  are  found  to  obey  no  law,  and  to 
be  purely  accidental  in  occurrence.  With  strong  papers  made 
with  long  fibres  he  found  about  6  per  cent,  variation  in  the 
elasticity  test  and  about  3  per  cent,  in  the  tearing  test. 

An  interesting  account  is  given  by  Herzberg  in  1893  of  a 
wood  pulp  paper  made  in  1852.  From  his  statement  it  would 
appear  that  so  long  as  the  paper  was  kept  away  out  of  the  action 
of  air  and  light  it  remained  to  all  appearances  unchanged.  But 
although  it  appeared  to  be  unchanged,  it  might  be  said  potentially 
to  have  changed  in  some  way,  because  strips  of  paper  exposed  to 
direct  sunlight  for  a  period  of  20  hours  showed  a  decided  change 
in  colour.  This  would  hardly  have  occurred  with  chemical  wood 
pulp  freshly  made. 

In  1894,  Herzberg  gave  particulars  of  English,  German,  and 
French  blotting  papers,  and  the  mode  of  testing  them  for  their 
bibulous  properties,  as  proposed  by  Winkler.  This  is  based  upon 
the  height  to  which  water  will  be  drawn  up  by  a  strip  of  paper  in 
a  definite  period  of  time,  when  the  paper  is  suspended  vertically, 
with  its  bottom  edge  just  touching  the  surface  of  the  water. 
The  strips  were  15  mm.  broad,  and  the  time  allowed  was  ten 
minutes.  He  divides  the  paper  into  two  classes.  Those  which 
draw  up  over  100  mm.  and  those  which  draw  up  over  60  mm. 
At  that  date  the  English'  blotting  papers  showed  very  much  the 
best  results,  the  German  and  French  being  much  inferior  in 
bibulous  qualities. 

As  regards  the  presence  of  mineral  matter,  this  seems  to 
be  less  important  than  it  was  commonly  supposed  in  its  effect 
upon  the  absorbent  qualities  of  blottings,  although  the  best 
qualities  of  all  contain  little  or  none. 

It  will  be  interesting  to  note  at  this  date  that  all  the  papers 
examined,  with  the  exception  of  two,  were  made  of  cotton  fibres 
alone. 

A  further  examination  of  blotting  paper  was  made  in  1896 
of  a  much  larger  number.  The  mode  of  testing  was  the  same, 
althought  the  I’esults  were  expressed  somewhat  differently.  In 
this  series  the  English  makers  did  not  show  up  to  the  same 
relative  advantage.  The  tests  showed  a  great  improvement  in 
foreign  makes,  as  compared  with  the  English,  and  a  change  in  the 
composition  of  the  blotting  papers  made.  Out  of  89  papers,  42 

E 


130 


were  made  of  cotton  fibres  alone,  whilst  the  remaining  47 
contained  in  their  composition  more  or  less  of  the  following : 
linen,  wool.  wood.  In  one  case  mechanical  wood  pulp  was  noted. 

It  appears  now  from  recent  samples  which  have  been 
submitted  to  me  that  papers  of  most  excellent  bibulous  quahties 
can  be  produced  from  linen  alone,  and  also  from  a  certain  class 
of  wood  pulp,  if  the  same  are  carefully  and  suitably  treated. 

We  next  come  to  the  question  of  physical  change  and 
alterations  in  papers  by  heat  and  moisture. 

The  question  was  studied  by  G.  Dalen.  The  conclusions  to 
be  drawn  from  his  tests  are  as  follows  : — That  for  percentages 
of  moisture  between  0  per  cent,  and  80  per  cent,  of  saturation, 
paper  increase  in  length  in  direct  proportion  to  the  amount  of 
moisture  present.  But  when  the  degree  of  moisture  ranges 
between  80  per  cent,  and  100  per  cent,  the  expansion  is  somewhat 
over  proportion.  The  longitudinal  is  less  than  the  transverse 
expansion. 

The  effect  of  temperature  is  less  than  that  of  moisture, 
favouring  expansion  when  associated  with  percentages  up  to  65 
of  saturation,  but  retarding  it  beyond  that  degree. 

Furthermore,  there  appears  to  be  no  permanent  linear 
alteration  in  air  containing  less  than  80  per  cent,  saturation. 
Under  ordinary  conditions  the  question  of  temperature  for  all 
practical  purposes  is  by  no  means  an  important  one,  because  we 
only  use  paper  up  to  a  temperature  of  say  90°  Fahr.  in  the 
English  climate.  The  results  with  higher  temperatures,  therefore, 
are  of  scientific  rather  than  practical  value.  With  moisture, 
however,  it  is  different,  as  we  often  have  very  moist  atmospheres, 
and  near  the  point  of  complete  saturation. 

Next  we  come  to  the  question  of  the  effect  of  sunlight  on  the 
size  contained  in  paper.  This  has  a  direct  practical  tearing,  but 
I  venture  to  think  that  we  must  accept  the  statements  made  by 
investigators  on  this  subject  with  a  good  deal  of  reserve.  I  will, 
however,  give  you  Herzberg's  opinions  which  he  expressed  in 
1896: — He  exposed  papers,  both  rosin  and  gelatine  sized,  to  the 
action  of  sunlight,  covering  certain  portions.  At  the  end  of  the 
experiment  the  covered  parts  of  the  rosin-sized  paper  proved  to 
have  kept  their  size,  whilst  that  exposed  had  lost  it.  Both  the 
covered  and  uncovered  parts  of  the  animal-sized  papers  had 
deteriorated.  This  proves,  he  says,  that  in  the  case  of  rosin-sized 
papers  it  is  light  which  causes  the  deterioration,  but  with  animal- 
sized  papers  it  is  some  other  destructive  agent.  He  finds  no  loss 
of  size  either  with  gelatine  or  rosin  papers  on  exposure  to  a 


131 


temperature  approaching  that  of  boiling  water  for  a  sufficient 
length  of  time  to  disintegrate  the  fibres. 

It  is  supposed  that  the  rosin  on  exposure  to  the  sun  is 
either  destroyed  or  converted  into  something  else.  It  certainly 
is  not  extractable  by  ordinary  chemical  solvents.  Rosin  size,  even 
when  sealed  up,  I  know  from  long  experience,  changes  entirely 
on  exposure,  and  becomes  insoluble.  A  lump  of  rosin  will 
become  pulverised.  Added  to  this  we  have  the  fact  that  the  rosin 
has  a  deleterious  and  weakening  effect  upon  even  rag  paper  on 
exposure,  which  shows  rosin  to  be  a  very  fickle  substance  under 
such  conditions. 

Herr  O,  Winkler,  of  the  Leipsic  Paper  Testing  establishment, 
has  made  a  study  of  the  action  of  air  and  sunlight  on  printing 
papers  free  from  wood,  the  results  of  which  were  published  in  1893. 

He  made  cuttings  of  the  cellulose  and  cellulose  papers  and 
exposed  them  for  some  days  during  the  month  of  May  to  direct 
sunlight.  Other  cuttings  were  hung  for  24  hours  in  the  vapour 
of  nitric  acid  and  then  treated  with  ammonia. 

Winkler  employed  this  method  for  some  years  to  ascertain 
the  tendency  of  paper  to  change  colour  and  become  brown  on 
exposure.  A  more  or  less  pronounced  change  takes  place  in  the 
whiteness  of  papers  free  from  wood  after  they  are  saturated  with 
rosin  size  and  submitted  to  this  chemical  treatment.  The  presence 
of  the  size  seems  to  degrade  the  colour.  It  has  been  established 
that  atmospheric  air  has  no  influence  on  the  colour  of  pure 
cellulose  paper  unsized  and  free  from  wood. 


E 


LECTURE  X.  (Part  II.) 


SUNDRY  PHYSICAL  QUALITIES  OF  PAPER  ( continued ). 

H.M.  Stationery  Office  contracts — National  Physical  Laboratory — Work  in 
Italy — Banknotes — Work  in  United  States  and  Sweden — Climatic  and 
local  conditions  affecting  requirements — Drawing  papers — Improvement 
on  storage  of  papers — Effects  of  time  on  stretch,  and  strength — Question 
of  bulk — Influence  of  glazing  on  bulk — Effects  of  mineral  constituents  on 
bulk — Influence  of  glazing  on  appearance — Action  of  light  on  papers — 
Transparency — Opacity — Methods  for  determining  opacity — Necessity  for 
a  uniform  method. 


I  am  indebted  to  Mr.  E.  Stallybrass,  assistant  examiner  of 
paper  to  H.M.  Stationery  Office,  for  information  in  regard  to  the 
requirements  of  the  Stationery  Office  for  certain  classes  of  paper. 

The  method  adopted  by  the  Stationery  Office,  although  very 
different  to  the  recommendations  made  by  either  the  committee 
of  the  Society  of  Arts  appointed  in  London  or  the  Government 
testing  stations  at  Charlottenbnrg,  appear  to  me  thoroughly 
practical,  if  not  scientific. 

With  class  2  of  the  “  schedule  of  papers  required  for 
stock,”  which  are  “  writings,  air  dried,”  the  mean  breaking  strain 
and  mean  stretch  required  are  given  for  each  paper.  The  figures 
represent  the  mean  results  obtained  for  both  directions  of  the 
sheet,  and  are  calculated  on  a  strip  of  paper  five-eighths  of  an  inch 
wide ,  and  having  a  free  length  of  seven  inches  between  the  strips. 
By  specifying  the  mean  breaking  strain  as  well  as  the  mean 
stretch  required  on  a  given  width,  with  a  given  distance  between 
the  clips  for  this  class,  the  Stationery  Office  can  ensure  having 
papers  answering  to  these  special  requirements,  at  any  rate  the 
conditions  of  the  test,  a  specific  which  is  more  than  can  be  said 
of  the  German  method. 

Class  3  are  ordinary  writings,  machine  made,  animal  tub-sized, 
but  there  are  no  special  requirements  as  regards  strength  and 
breaking  strain  specified,  except  with  tobacco  band  paper,  where  it 
is  stated  that,  this  paper  being  required  for  printing  from  the 


133 


plate,  it  is  essential  that  the  sheets  should  be  uniform  in  texture 
and  free  from  fibre-knots  and  other  hard  particles. 

Class  5. — Blotting  papers.  Specified  to  be  all  rag,  machine 
made,  and  free  from  loading. 

Class  6. — Printing  and  lithographic  papers.  General  speci¬ 
fication,  rolled,  machine  made,  engine-sized,  loading  not  to  exceed 
15  per  cent. 

Certain  of  the  papers  of  this  class  are  required  to  be  free  from 
stretch  when  used  for  colour  lithography. 

Class  9. — Brown  papers,  air-dried.  Specification,  air-dried, 
machine  made.  For  this  class  the  mean  breaking  strain  and  mean 
stretch  required  are  given  for  each  paper.  The  figures  represent 
the  mean  of  the  results  obtained  for  both  directions  of  the  sheet, 
and  are  calculated  on  a  strip  of  paper  tivo  inches  i vide,  and  having 
a  free  length  of  seven  inches  between  the  strips.  In  case  of  papers 
indicating  a  higher  breaking  strain  than  the  minimum  required, 
a  proportionate  increase  in  the  stretch  must  be  shown. 

jNbte  the  difference  between  the  width  of  the  strip  in  this 
case  and  the  previous  one  cited. 

I  am  informed  that  the  reason  for  insisting  upon  a  strip  of 
two-inch  width  here  is  that  it  is  found  by  experience  that  for  the 
coarser  kinds  of  paper,  such  as  browns,  which  always  contain  thin 
spots,  a  five-eighth  inch  strip  is  not  wide  enough  to  get  a  fail- 
idea  of  the  general  strength.  The  result  is  that  a  narrow  strip 
will  only  indicate  the  strength  of  the  thin  spots,  which  is  by  no 
means  a  fair  criterion  of  the  general  strength  of  the  paper.  It  is 
not  thought  that  within  certain  limits  these  thin  papers,  when 
surrounded  by  thicker  portions,  materially  detract  from  the 
strength  of  the  paper  when  in  actual  use.  These  considerations 
have  led  H.M.  Stationery  Office  to  take  a  wider  strip  for  this 
class  of  paper. 

Class  10. — Brown  papers,  cylinder-dried.  General  specifi¬ 
cation,  machine  .made.  As  regards  the  length  and  width  of  strip 
for  taking  the  breaking  strain,  this  is  the  same  as  for  class  9  ;  but 
note  that  it  differs  from  that  class  in  that  no  “  mean  stretch  ”  is 
specified,  and  for  this  reason  it  is  found  that  the  stretch  of  a 
paper  is  to  a  great  extent  an  index  to  the  amount  of  handling  it 
will  stand.  One  paper  may  show  a  much  greater  breaking  strain 
than  another,  and  yet  may  not  stand  nearly  so  much  handling. 
This  would  be  due  to  the  latter  being  more  elastic.  As  class  9 
papers  are  required  to  be  practically  durable,  it  has  been  found 
advisable  to  specify  the  stretch.  Class  10  papers  are  used  when 


134 


great  durability  is  not  required,  and  it  has  not  been  found 
necessary  to  specify  the  stretch. 

For  fine  papers,  on  the  other  hand,  such  as  class  2  above 
referred  to,  it  is  considered  necessary  to  have  a  uniform  thickness 
all  over  the  sheet,  and  thin  spots  are  a  decided  drawback,  hence 
it  is  that  narrower  strips  are  specified  for  the  strength  test. 

Chemical  wood  must  not  be  used  in  the  manufacture 
of  any  papers  with  the  exception  of  engine-sized  coloured 
printings  and  buff  papers,  where  an  addition  up  to  25  per  cent, 
will  be  allowed.  All  animal  tub-sized  papers  are  required  to  be 
as  far  as  possible  free  from  earthy  matter,  and,  except  where 
specially  stated,  the  amount  of  loading  added  to  other  papers  must 
not  exceed  6  per  cent. 

When  sulphite  or  soda  wood  are  used  either  separately  or 
conjointly  in  the  manufacture,  the  quality  of  neither  material 
shall  separately  exceed  50  per  cent. 

I  am  furthermore  informed  that  for  documents  which  are 
required  to  last  as  long  as  possible,  such  as  certificates  of  births, 
deaths,  and  marriages,  &c.,  the  Stationery  Office  adhere  to  hand¬ 
made  paper. 

For  documents  of  next  importance  are  used  air- dried  and 
tub-sized  paper  made  entirely  of  rags. 

For  Blue  Books  ordinary  printings  are  used,  which,  however, 
are  required  to  be  free  from  chemical  wood,  and  not  to  contain 
more  than  15  per  cent  of  loading. 

The  Stationery  Office  have  a  particularly  strong  hand-made 
loan  paper  which  is  used  for  documents  which  are  subjected  to  a 
good  deal  of  handling,  such  as  tickets  of  leave. 

The  “  National  Physical  Laboratory  ”  has  recently  been 
established  at  Bushey  House,  Teddington,  by  His  Majesty's 
Government  for  standardising  and  verifying  instruments,  for 
testing  materials,  and  for  the  determination  of  physical  constants. 
The  laboratory  is  intended,  like  the  Riechsanstalt  in  Berlin,  to 
have  the  authority  of  a  national  institution,  and  does  not  seek  to 
interfere  with  local  institutions. 

1  am  indebted  to  the  director,  Dr.  B.  T.  Gflazebrook,  F.R.S., 
for  information  as  to  what  is  contemplated  as  far  as  paper  is 
concerned.  In  the  physical  department  the  testing  work  includes, 
among  other  experiments,  No.  VIII.,  “  Chemical  and  Microscopic 
Tests  of  Papers  and  Similar  Materials.” 

I  am  informed  that  the  National  Physical  Laboratory  are 
making  arrangements  for  the  ordinary  chemical  and  microscopical 
examination  of  papers  of  a  good  class,  and  this  will  be  extended 


135 


to  papers  of  other  classes  if  there  seems  to  be  a  demand.  The 
tests  will  be  undertaken  for  a  fixed  fee. 

An  interesting  series  of  articles  has  recently  been  translated 
from  the  Italian  and  published  in  the  Paper  Trade  Beview, 
dealing  with  the  preservation  of  Italian  State  papers,  and  giving 
the  official  tests,  by  Dr.  Scavia  in  Beyista  Tecnica.* 

He  states  that,  notwithstanding  the  remarkable  progress 
made  during  the  last  30  years  in  the  machinery  and  chemistry  of 
the  paper  industry,  there  has  been  a  general  decline  in  the 
articles  manufactured,  especially  from  the  point  of  view  of 
durability.  With  this  remark  I  think  most  people  will  agree. 
He  quotes  Professor  Loevinson : — “  Lamentable  experience 
demonstrates  continuously  that  light  of  too  great  intensity  or 
humidity,  cold,  and  insects,  in  addition  to  the  use  of  inferior 
qualities  of  size  and  materials  for  bindings,  are  the  most  inveterate 
enemies  of  those  printed  and  written  documents  which  should 
resist  as  long  as  possible  the  injurious  action  of  time.” 

Dr.  Scavia  states  that  “  The  continuous  deterioration  of 
printed  and  written  documents,  the  consequence  of  utilising  such 
a  quality  of  paper,  which  can  also  be  demonstrated  by  chemical 
tests,  would  necessarily  lead  to  complete  and  irreparable  decay  at 
a  more  or  less  distant  time.” 

An  account  is  given  of  the  work  aided  by  the  Turin  Chamber 
of  Commerce,  working  for  the  object  to  which  it  owes  its  existence — 
for  analysing  and  testing  different  kinds  of  paper,  raw  materials, 
&c. — and  it  is  stated  that  in  addition  to  a  description  of  the 
different  appliances  used  for  testing,  a  small  plant  was  installed 
for  experimental  and  educational  work  to  make  hand-made  paper. 

“  It  is  not  a  question  of  adopting  normal  types  of  papers 
bearing  appropriate  figures  and  water-marks  like  a  normal  ‘papier’ 
in  Prussia,  t  We  must  not  place  useless  difficulties  in  the  ivay  of 
industry,  nor  suddenly  shaclde  it  by  a  regular  disciplinarian  system. 
It  is  merely  requisite  to  study  the  various  current  types  of  paper 
employed  by  various  administrations,  examine  their  defects  from 
the  point  of  view  of  durability  and  resistance,  and  fix  a  technical 
data  with  which  the  new  paper  should  comply,  within  certain 
limits,  in  tests  at  the  government  laboratory.” 

This  is  somewhat  awkardly  expressed,  but  the  meaning  is  very 
clear.  I  think  we  must  agree  that  the  German  system  is  far  too 
rigid,  or  shall  I  say  impracticable  ?  It  does  not  appear  that 
normal  papers  are  required  so  much  as  a  practical  system  of 


*  See  Paper  Trade  Review,  Vol.  38,  Nos.  14,  15,  and  16. 
t  The  italics  are  mine. 


136 


testing.  His  Majesty’s  Stationery  Office  have  adopted  a  practical 
system  (as  above  described)  in  a  few  instances,  but  the  system 
needs  to  be  extended.  These  tests  should  not  hamper  the  paper- 
maker,  but  merely  be  the  means  of  compelling  him,  or  I  would 
rather  put  it,  aiding  him  in  keeping  up  a  certain  standard  of 
quality,  sufficient  merely  for  the  purpose  for  which  the  paper  is 
used,  and  as  a  safeguard  to  the  stationer  and  printer,  who  have 
a  right  to  know  something  of  the  composition  and  physical 
properties  of  the  paper  they  purchase. 

In  the  table  communicated  by  Dr.  Scavia,  showing  the 
various  papers  used  for  particular  purposes  and  their  compositions, 
the  rag  papers  certainly  show  the  best  results,  not  only  as 
regards  breaking  strain,  but  also  as  regards  resistance  to  compres¬ 
sion.  It  is  pointed  out  that  the  effects  of  such  tests  would  be  that 
the  Government  would  buy  an  article  on  such  tests  and  not  on  the 
system  of  manufacture.  It  certainly  does  seem  that  what  should 
concern  the  buyers  most  is  the  quality  of  the  paper  and  not  the 
system  of  manufacture. 

As  regards  the  conditions  for  drawing  papers,  it  is  stated  that 
the  paper  must  not  have  an  alkaline  reaction ;  but  a  very  slight 
acid  reaction  with  blue  litmus  can  be  tolerated,  provided  that  this 
is  due  not  to  acids  but  to  neutral  salts  which  change  the  colour  of 
litmus.  Elongation  must  not  be  more  than  6  per  cent. 

The  same  translation  in  discussing  the  special  methods  and 
qualifications  of  banknotes  in  different  countries,  and  the  means 
adopted  to  prevent  fraud,  states  :  “  Amongst  nations  and 

institutes  which  give,  so  to  speak,  equal  importance  to  printing 
and  paper,  Bussia  is  the  chief.  The  Eussian  type  of  banknote 
may  be  regarded  as  the  most  perfect  in  existence.” 

From  experiments  made  with  various  kinds  of  notes,  it  is 
considered  that,  with  due  regard  to  what  has  been  said,  a  good 
type  can  be  obtained,  especially  small  notes,  when  the  following 
conditions  are  fulfilled  :  — 

Average  rupture  strain  . .  8  to  9  kilos. 

„  „  length  .  .  6,000  to  7,000  m. 

„  elongation  per  cent.  9  to  11. 

Percentage  of  ash  .  .  .  .  Less  than  3. 

Eesistance  to  crushing  with  3,000  to  5,000  revolutions  of  the 
Schopper  dynamometer  and  a  strain  of  one  kilo,  on  the  springs. 

A  test  of  crushing  “  notes  ”  gave  the  following  results  : — 
Average  rupture  strain  .  .  5.04  kilos. 

„  „  length  .  .  4,318  m. 

„  elongation  per  cent.  6.29 
Percentage  of  ash  .  .  .  .  2.43 


137 


As  regards  what  the  various  countries  are  doing  for  the 
establishment  of  tests  there  is  not  much  information  available. 
Germany  we  know  all  about.  I  have  already  referred  to  what  little 
is  being  and  has  been  done  in  this  country,  and  we  have  just 
spoken  of  Italy. 

It  is  not  unlikely  that  the  United  States  will  give  us  a  lead. 
It  is  reported  from  Washington,  D.C.,  that  the  Bureau  of  Forestry 
has  established  a  testing  office  in  co-operation  with  the  Bureau 
of  Chemistry.  Particular  attention  will  be  given  to  the  study  of 
woods ;  also  a  study  has  been  planned  of  the  composition  and 
physical  characteristics  of  the  various  papers  containing  either 
mechanical  or  chemical  wood  pulp  which  are  found  on  the 
American  market.  The  ultimate  object  of  this  work  is  the 
establishment  of  a  paper-testing  laboratory  similar  to  that  now 
being  operated  by  the  German  Government .  at  Berlin.  The 
necessity  of  such  a  laboratory  is  apparent  when  it  is  considered 
that  practically  all  official  publications  are  now  printed  on  such 
paper,  and  that  the  life  of  wood  pulp  papers  is,  in  general,  very 
brief.  The  importance  of  certain  standards  is  self-evident,  and  it 
is  hoped  to  establish  and  enforce  these  for  American  papers,  at 
least  where  they  are  furnished  to  the  Government. 

I  have  it  on  good  authority  from  a  large  firm  in  Sweden  that 
there  will  be  in  the  neav  future  new  regulations  with  regard  to  the 
manufacture  of  paper  for  the  Swedish  Government.  The  promised 
new  regulations  are  to  a  great  extent  in  accordance  with  the  old 
German  standards,  and  allow  the  use  of  mechanical  and  rosin¬ 
sized  paper  even  for  documents  that  ought  to  be  of  unlimited 
durability.  I  have  been  engaged  on  behalf  of  a  large  firm  in 
Sweden  to  report  upon  the  whole  subject.  It  is  to  be  hoped  that 
the  Swedish  Government  will  safeguard  themselves  against 
inferior  qualities  for  permanent  documents. 

The  question  of  paper  standards  or  standard  methods  for  the 
examination  and  testing  of  papers  for  different  countries  requires 
a  knowledge  of  special  circumstances  and  conditions.  The 
question  is  affected  by  climatic  conditions.  In  a  hot  and  humid 
climate  it  is  absolutely  necessary  that  something  should  be  added 
to  the  paper  to  prevent  its  putrefaction.  In  England  this  can 
hardly  be  said  to  be  the  case.  Papers  have  to  be  specially  prepared 
for  the  Indian  market.  Then,  of  course,  the  question  of  the 
individual  requirements  of  the  country  have  to  be  taken  into 
consideration. 

But  I  do  not  wish  it  to  be  inferred  that  papers  always  tend 
to  deteriorate  if  kept  for  any  length  of  time  ;  fortunately  the 


133 


reverse  is  the  effect  in  certain  instances.  Some  papers  are  very 
much  improved  by  keeping.  A  more  exact  knowledge  of  these 
improvements,  as  well  as  conditions  which  effect  changes  in  papers 
resulting  in  improvement,  should  be  very  helpful  to  the  buyers 
and  sellers  of  papers.  This  subject  was  discussed  in  the  columns 
of  Papee  aki)  Pulp,  in  the  correspondence  class  which  I  conducted 
this  year. 

The  leading  water-colour  artists  know  what  they  want  in  the 
way  of  paper,  but  they  find  that  they  do  not  always  get  what  they 
want.  Some  years  ago  when  this  controversy  was  going  on  about 
the  so-called  acid  action  of  drawing  papers,  I  was  invited  to  the 
Savage  Club  to  meet  one  or  two  well-known  men  who  volunteered 
to  give  me  their  experiences  and  state  their  requirements,  with  a 
view  of  influencing  papermakers  to  produce  what  they  wanted. 

It  is  a  well-known  fact  that  certain  drawing  papers  of 
certain  dates  by  a  well-known  maker  are  very  much  prized  by 
artists.  A  well-known  artist  informed  me  that  this  improvement 
is  in  what  is  technically  called  the  “  tooth  ”  of  the  paper  and  is 
the  result  of  ageing.  In  this  case  we  have  an  improvement  in 
the  surface  of  the  paper  which  is  brought  about  by  ageing  or 
stocking,  but  it  is  evident  that  papers  even  of  similar  composition 
age  differently,  because  the  makes  of  some  years  improve  on 
ageing,  whereas  the  makes  of  other  years  do  not,  at  any  rate  to 
the  same  extent.  This  appears  to  be  an  uncertain  quantity,  very 
much  like  the  ageing  of  wine. 

Gelatine  papers,  especially  those  which  are  dried  hastily,  are 
also  improved  considerably  in  many  instances  by  keeping  in  stock, 
during  which  time  the  gelatine,  which  should  finally  contain  about 
17  per  cent,  of  air-dried  moisture,  resumes  its  atmospheric 
condition.  This  improvement  can  be  better  realised  by  noting 
the  effect  of  moisture  upon  a  sheet  of  gelatine.  The  gelatine  in 
a  dry  air  or  if  placed  in  the  sun  is  liable  to  become  very  brittle,  but 
on  removing  it  to  an  ordinary  atmosphere  in  the  cool  it  resumes 
its  strength  and  toughness.  The  same  undoubtedly  takes  place, 
in  a  measure  at  any  rate,  in  regard  to  the  microscopic  films  of 
gelatine  in  tub-sized  papers. 

Many  papers,  such  as  “  browns, v  improve  both  in  feel  and 
strength  and  general  qualities  when  kept  in  stock.  I  believe  it  is 
not  an  uncommon  thing  for  a  buyer  of  paper  to  reject  browns 
and  return  them  to  the  mill  as  not  being  up  to  sample,  but  on  the 
same  parcel  being  tendered  to  him  a  few  months  later,  he  has 
been  known  to  accept  the  paper  and  find  it  perfectly  satisfactory. 
This  is  the  result  of  a  change  which  has  taken  place  in  the  paper 


139 


itself,  partly  due  to  the  paper  becoming  restored  to  its  natural 
condition  as  regards  moisture,  but  especially  owing  to  the  fibres 
settling  thenselves  down  and  a  certain  amount  of  expansion  or 
contraction  taking  place  in  the  paper  itself,  as  it  settles  down  to 
its  normal  condition,  resulting  in  the  final  production  of  a  more 
natural  sheet.  This  is  by  no  means  an  easy  question  to  explain, 
but  from  general  experience  it  has  become  a  well-known  fact. 

I  would  suggest  that  the  following  conveys  a  better  idea  of 
what  change  or  changes  take  place  under  such  conditions.  A 
machine-made  cylinder-dried  brown  is  essentially,  as  the  name 
conveys,  an  artificial  paper,  i.e.,  the  felting,  stretching,  and  drying 
are  done  under  conditions  that  are  not  at  all  natural  to  the 
felting  and  drying  of  the  fibre.  It  results  from  this  that  the 
fibres  of  paper  so  produced  are  in  a  state  of  tension,  and  attempt 
to  resume  their  natural  shape  and  position.  On  storing,  this 
paper  takes  up  moisture  and  the  fibres  by  slow  degrees  draw  into 
their  natural  positions.  The  result  is  that  the  paper  is  often 
much  improved  in  strength,  feel,  and  surface,  although  common 
experience  seems  to  indicate  that  the  stretch  is  often  diminished 
with  some  printing  papers. 

The  following  results  .quoted  by  one  of  those  who  entered 
the  correspondence  class  instituted  by  Paper  asd  Pulp  show  an 
improvement  in  the  breaking  strain  due  to  storing  for  10 
months,  accompanied  by  an  increase  in  weight  of  3  per  cent., 
although  it  shows  a  diminution  in  the  breaking  tension.  This 
confirms  the  opinion  of  a  previous  investigator. 

“  I  once  tested  a  tub-sized  paper  for  strength  and  then 
carefully  rolled  the  sheets  and  laid  them  on  a  high  shelf  where 
air,  but  diffused  light  only,  could  reach  them.  Ten  months  later  I 
again  tested  them.  The  following  are  the  figures  : — 

Original  Trial.  Second  Trial. 

Breaking  Strength. 

Average  Dn.  and  Ac.  Me.  3.781  km.  4.145  km. 

Breaking  Expansion  ...  5  %  3.6  % 

Increase  of  weight  =  3  %  ” 

As  regards  the  loss  of  finish  or  storage,  it  is  remarked  by  one 
writer  that : — 

“  On  the  other  hand,  M.F.  papers,  if  kept  long  in  stock, 
especially  in  a  cool  room,  will  go  back  in  finish  owing  to  the  fibres 
being  expanded.  [In  this  connection  I  might  say  soft-sized  papers 
will  lose  their  finish  quicker  than  hard-sized,  and  printings  quicker 


140 


than  writings,  the  presence  of  the  size,  especially  if  it  be  rosin, 
preventing  an  undue  amount  of  moisture  from  being  absorbed. 
The  colour  also  will  fade,  and  the  sheet  will  have  a  “  dulness  ” 
which  newer  ones  do  not  have.  The  colour  will  fade  more  rapidly 
in  seaside  places,  due,  I  suppose,  to  the  larger  quantity  of  oxygen 
in  the  air  acting  in  conjunction  with  moisture.] 

“  All  papers  on  absorbing  moisture  stretch  a  little  in  both 
directions,  i.e.,  along  the  direction  of  the  web  and  across,  but 
principally  across.  Therefore  if  a  paper  is  lithographed  without 
being  properly  matured  it  runs  a  great  chance  of  stretching  during 
the  interval  between  the  impressions,  throwing  the  final  impressions 
out  of  register. 

“  Note  direction  of  curl,  which  invariably  takes  place  parallel 
to  direction  of  web.” 

The  improvement  to  envelope,  litho,  and  printing  papers  is 
chiefly  due  to  the  equalisation  of  moisture  as  affecting  their  after¬ 
behaviour. 

Envelope  papers  are  improved  by  lying  in  stock,  as  this  cures 
the  tendency  to  “curl,”  which  causes  great  annoyance  to  the 
envelope  manufacturers  when  feeding  the  dies  into  the  folding  and 
gumming  machines.  The  curling  is  due  to  the  moisture  from 
the  air  getting  in  at  the  edges  of  the  sheets  ;  if  exposed  a  sufficient 
time  the  sheets  will  absorb  the  moisture  uniformly  all  over  the 
sheet  and  curling  is  remedied. 

Newspapers  and  common  printings  are  well  known  to  improve 
by  keeping  for  a  short  time,  the  paper  working  much  better  and 
taking  the  ink  from  the  type  easier,  so  as  to  produce  a  well-printed 
sheet.  The  reason  for  this  is  that  the  paper  often  leaves  the 
maclune  too  dry,  and  when  in  contact  with  the  atmosphere  for 
some  time  the  paper  becomes  air-dried,  or  damper  than  when 
it  left  the  machine,  and  damp  paper  always  prints  better  than  dry, 
absorbing  the  ink  better. 

The  question  of  bulking,  as  affected  by  composition  and 
treatment  of  fibres,  is  outside  the  scope  of  this  lecture,  but  the 
question  of  reduction  of  bulk  as  affected  by  glazing  might  be 
briefly  referred  to  as  belonging  rather  to  the  domains  of  the 
finished  paper.  I  give  some  results  supplied  during  the  corre¬ 
spondence  class,  as  giving  some  idea  of  the  reduction  in  bulk 
with  different  finishes.  These  figures  would  of  course  vary 
considerably  with  different  finishes  and  compositions ;  they  give 
some  idea,  however,  of  the  effects  of  compression  upon  paper. 
The  following  are  the  results  of  four  papers  tested  for  bulk, 


141 

all  of  same  weight  (30  lbs.  demy,  480  lbs.),  and  same  furnish 
including  loading : — 

Thick-  Loss  in 
ness,  thick- 
1=100.  ness. 

%  % 

1.  Rough  antique  finished,  6.0  thousandth  of  an  inch  100  0 

2.  Best  machine  finished  4.6  „  ,,  76  24 

3.  Plate-glazed  ...  3.8  ,,  ,,  63  37 

4.  Super-calendered  ..3.5  ,,  „  58  42 

Other  factors  being  equal. 

The  presence  of  clay  affects  the  question  of  bulk.  Mineral 
does  not,  at  any  rate  as  a  rule,  add  to  the  bulk  of  a  paper.  If, 
therefore,  you  have  two  papers  containing  each,  say,  10  per  cent, 
of  mineral,  A  10  per  cent,  of  clay,  B  10  per  cent,  of  baryta, 
each  of  them  contains  90  per  cent,  of  fibrous  material,  and  if  this 
fibrous  material  is  the  same  for  the  two  papers  in  every  respect, 
the  bulking  of  these  two  papers  will  be  the  same.  Neither  the 
clay  nor  the  baryta  add  to  the  bulk,  but  simply  tend  to  fill  the 
interstices.  The  clay  being  of  lower  specific  gravity  than  the 
baryta,  and  consequently  occupying  a  greater  space  for  a  given 
weight,  will  fill  the  paper  to  a  greater  extent  than  the  baryta,  but 
neither  will  bulk  the  paper.  I  do  not  wish  to  assert  that  papers 
containing  a  very  large  proportion  of  mineral  matter  are  not 
increased  in  bulk  thereby,  but  within  reasonable  limits  the 
mineral  simply  fills  the  paper  and  diminishes  the  air-spaces.  Of 
course  when  you  come  to  a  paper  heavily  loaded,  the  air-space 
of  which  is  largely  closed  by  the  mineral  matter,  it  will  not 
diminish  in  bulk  to  the  same  extent  at  the  super-calenders  as  an 
unloaded  one.  This  stands  to  reason  from  what  has  been  already 
stated.  Furthermore,  it  stands  to  reason  that  two  papers,  A 
containing  25  per  cent,  of  clay  and  B  containing  25  per  cent,  of 
baryta,  B  could  be  reduced  in  thickness  more  on  super-calendering 
than  A.  All  these  points  are  of  interest  and  of  some  practical 
moment,  and  a.  thorough  mental  grasp  is  a  desideratum. 

The  behaviour  of  paper  towards  light  demands  special  study. 
All  papers  may  be  said  to  be  translucent,  that  is,  they  are  neither 
completely  transparent  nor  completely  opaque,  some  tend  in  one 
direction  whilst  others  tend  in  the  other  direction.  This  property 
of  partly  transmitting  and  partly  reflecting  light  is  characteristic 
of  all  papers.  The  character  of  the  surface  imparted  to  the  paper 
would  affect  the  question  considerably.  Supposing  you  plate- 
glaze  a  paper  and  crush  it,  you  certainly  would  not  get  the  same 
result  as  regards  transparency  as  if  you  super-calendered  it,  or  as 
if  you  friction-glazed  it  on  one  surface  only.  Each  of  these  papers 
would  be  differently  affected  as  regards  the  question  of  trans¬ 
parency.  Some  kinds  of  glazing  may  be  said  to  affect  only  the 


142 


surface  of  the  paper  and  not  the  interior.  Plate-glazing  may  be 
said  to  affect  the  whole  of  the  fibres. 

Let  us  deal  with  the  subject  from  the  point  of  view  of 
opacity,  and  endeavour  to  obtain  an  optical  explanation  of  opacity 
of  paper  and  see  how  it  can  be  measured. 

The  fact  that  colour  fades  more  quickly  at  seaside  places  may 
be  due  to  the  fact  that  there  is  a  greater  amount  of  ozone  (not 
oxygen)  in  the  air,  combined  with  a  greater  amount  of  moisture. 
The  amount  of  oxygen  in  the  air,  whether  at  the  seaside  or  any 
other  place,  is  practically  constant,  but  the  amount  of  ozone 
varies,  and  is  greatest  at  seaside  places,  and  as  ozone  is  an  active 
bleaching  agent  and  requires  a  certain  amount  of  moisture  to  give 
it  its  greatest  activity,  it  is  highly  probable  that  the  fading  of 
papers  at  seaside  places  is  due  to  this  cause. 

Rosin-sized  Papers. — The  action  of  light  on  rosin-sized 
paper  gradually  produces  discoloration  in  proportion  to  amount 
of  rosin  they  contain. 

Discoloration. — The  discoloration  of  “  self-colour  ”  papers  is 
generally  brought  about  by  oxidation  of  the  non-cellulose  portion 
of  the  material,  but  with  some  rag  papers  where  this  was  formerly 
thought  to  be  the  case  it  has  been  due  to  the  excessive  quantity  of 
rosin  used.  This  is  acted  on  by  sunlight,  and  a  brown,  sandy 
colour  is  produced.  The  formation  of  sulphides  is  a  most 
objectionable  feature  with  ultramarine  coloured  papers,  and  this 
combined  with  the  action  of  alum  causes  the  colour  to  fade. 

You  want  some  slight  knowledge  of  the  science  of  colour  and 
optics.  To  gain  the  necessary  knowledge  you  could  not  do  better 
than  read  the  little  book  by  A.  H.  Church,  on  “Colour  '’  (Cassell  & 
Co.),  also  the  little  book  on  “  Colour  Measurement  and  Mixture,” 
by  Capt.  Abney,  published  by  the  Society  for  Promoting  Christian 
Knowledge,  but  if  you  find  even  these  two  books  too  much  foryou 
to  understand,  you  need  not  be  discouraged,  because,  although 
they  are  of  very  great  value  to  a  proper  understanding  of  the 
subject,  you  can  advance  your  knowledge  considerably  without 
them.  There  are  one  or  two  references  in  Church’s  book  to  the 
subject  of  paper.  “  When  the  rays  of  parallel  light  from  the  sun 
strike  upon  a  rough,  that  is,  an  unpolished  surface,  say,  of  a  piece 
of  white  paper,  they  are  incident  at  all  imaginable  angles,  with 
minute  surfaces  of  the  hollows  and  ridges  which  make  up  the 
reflecting  substance,  and  such  of  them  as  are  reflected  obey  the 
law,  but  are  reflected  in  a  countless  number  of  different 
directions.”  This  reflection  of  light  in  a  countless  number  of 
different  directions  by  the  small  fibres  which  compose  the  paper 


143 


is  the  real  cause  both  of  the  whiteness  and  opacity  of  papers. 
The  greater  these  countless  reflections  the  greater  the  opacity — 
the  less  the  transparency.  “  The  numerous  small  reflections  which 
occur  from  and  between  the  surfaces  of  the  felted  fibres  in  a  piece 
of  white  paper  may  be  greatly  lessened  by  wetting  or  oiling  the 
the  paper,  when  it  becomes  less  opaque,  and  at  the  same  time 
greyer  and  clearer ;  to  this  cause  the  transparency  of  tracing 
paper  and  tracing  cloth  is  due.” 

“  Bodies  are  said  to  be  transparent  when  they  permit  light 
to  pass  so  freely  as  to  allow  objects  to  be  perfectly  discerned 
through  them.” 

It  is  by  no  means  the  best  way  of  testing  the  transparency 
of  paper  to  hold  it  up  to  the  light.  Of  course,  if  we  hold  two 
papers  up  to  the  light,  the  one  which  appears  the  lighter  of  the 
two  is  the  more  transparent.  Wbat  we  want,  however,  is  some 
simple  mode  of  expressing  the  relative  transparencies  of  different 
papers,  and  some  simple  and  rapid  way  of  making  the  tests.  I 
will  briefly  describe  the  method  which  I  have  made  use  of  for  this 
puipose.  It  is  simple  and  does  not  require  any  scientific 
knowledge,  and  I  think  you  would  all  have  no  difficulty  in  making 
use  of  it. 

Take  a  piece  of  white  opaque  paper  printed  in  black  with  block 
letters.  If  you  take  two  papers,  one  of  which  is  transparent  and  the 
other  opaque,  the  letters  will  be  more  easily  read  through  the 
transparent  than  the  opaque  paper.  This  method  of  comparison 
is  of  course  different  to  holding  paper  up  to  the  light.  In  the 
method  I  am  describing,  the  light  has  to  pass  through  the  paper 
and  illuminate  it  sufficiently  so  that  the  background  is  discernible. 
The  light  has  to  pass  twice  through  the  paper,  first  to  illuminate 
the  background  and  back  again  from  the  background  to  the  eye. 
Now,  suppose  I  take  a  number  of  papers  of  the  same  composition 
exactly,  but  of  different  weights  per  ream.  Suppose  for  the  sake 
of  argument  they  are  fairly  thin  and  transparent  papers.  It  is 
merely  necessary  to  fold  each  a  sufficient  number  of  times  so  that 
it  just  renders  the  background  invisible.  Let  us  assume  that  A 
requires  to  be  folded  five  times,  B  seven,  and  C  eight.  The  one 
which  is  folded  the  greatest  number  of  times  is  the  most  trans¬ 
parent,  and  relatively  speaking  we  may  compare  the  transparencies 
of  these  papers  by  stating  the  number  of  folds.  The  relative 
transparencies  of  these  papers  would  therefore  be  five,  seven,  and 
eight  respectively. 

Now,  suppose  we  take  papers  of  different  materials  but  of 
equal  thickness,  and  desire  to  know  their  relative  transparencies. 


144 


We  take  a  case  in  point.  A  is  a  linen  bank  and  B  is  a  sheet  of 
tracing  paper  of  equal  thickness.  We  have  to  fold  A  five  times 
and  B  nine  times  before  we  obliterate  the  image  at  the  back. 
We  are  able  to  state  that,  thickness  for  thickness,  the  trans¬ 
parency  of  A  is  to  B  as  five  is  to  nine.  If  we  desire  another 
comparison,  we  can  take  papers  of  different  compositions  but  of 
equal  weights  (demy).  Now,  of  course,  it  does  not  follow  at  all 
that  these  papers  will  bulk  equally,  but  a  stationer  may  require 
to  substitute  one  paper  for  another  at  so  many  lbs.  demy.  He 
may  require  a  greater  capacity.  Now,  we  must  assume  again 
that  these  papers  are  fairly  thin.  A  requires  to  be  folded  twice 
and  B  three  times.  From  this  we  conclude  that,  weight  for 
weight,  the  transparency  of  A  is  to  B  as  two  is  to  three. 

Now  we  come  to  a  further  mode  of  treating  the  subject,  and 
one  which  will  enable  you  to  come  to  very  useful  and  definite 
conclusions  from  a  papermaker’s  standpoint  and  throw  a  lot  of 
light  on  the  question  we  have  been  discussing,  We  have,  for  the 
sake  of  example,  a  number  of  papers  of  different  compositions  but 
made  under  known  conditions.  Let  us  assume  that  we  wish  to 
determine  the  influence  of  china  clay  on  the  question  of  opacity 
in  an  esparto  paper.  We  know  the  ashes  of  the  different  papers  ; 
from  this  we  can  calculate  the  percentage  compositions  of  esparto 
and  clay.  It  is  not  necessary  that  these  papers  should  be  of 
equal  thickness.  We  take  each  of  them  in  turn  and  place 
them  over  the  background  as  before,  and  then,  by  means 
of  a  micrometer,  we  measure  the  thickness  of  each  paper 
necessary  to  extinguish  the  background.  The  one  which 
measures  the  thickest  is,  of  course,  the  one  which  is  most 
transparent,  and  the  one  which  measures  the  thinnest  is  the  least 
transparent,  thickness  for  thickness  with  the  others.  The 
micrometer  readings  expressed  either  in  thousandths  of  an  inch  or 
in  millimetres  will  express  the  relative  transparencies  of  these 
different  papers,  thickness  for  thickness ;  and  by  comparing  the 
compositions  with  these  figures  it  will  be  very  easy  to  arrive 
quickly  at  some  definite  conclusion.  The  same  modus  opercindi 
can  be  used  with  regard  to  other  mixtures  and  compositions.  If 
the  work  is  always  conducted  in  a  light  room,  but  not  in  direct 
sunlight,  one  series  of  operations  can  be  compared  with  the  other 
on  this  basis.  Such  figures  would  undoubtedly  be  of  great  value 
in  some  mills  where  the  question  of  transparency  and  opacity  is 
of  considerable  moment. 

I  notice  in  the  Paper  Trade  Eeview,  March  7th,  1902,  an 
account  of  a  method  employed  by  Mr.  O.  Winkler  for  the  deter- 


145 


urination  of  the  opaqueness  of  printing  papers,  which  is  very 
similar,  although  not  identical  with  that  which  I  employ.  I  am 
glad  to  see  that  Winkler  thinks  there  should  be  some  standard 
method  of  determining  the  opacity  of  paper,  to  be  agreed  upon  by 
the  buyers  and  sellers.  The  method  such  as  he  and  I  have  made 
use  of  might  very  well  be  employed  in  ordinary  commercial  practice. 
Apart,  however,  from  the  employment  of  such  a  method  by  buyers 
and  sellers,  it  would  be  of  the  utmost  value  to  many  manufacturers 
for  making  comparison  of  their  different  makes.  The  difference 
revealed  to  them  by  their  different  makes  and  compositions  would 
assist  them  in  determining  in  which  direction  to  work  both  for 
opaque  or  transparent  papers.  Much  of  the  difficulty  now 
experienced  by  manufacturers  is  due  to  the  roughness  and 
looseness  of  their  methods  of  comparison  giving  too  much  scope 
for  individual  bias,  and  introduces  an  uncertain  and  undesirable 
factor  which  chemists  generally  call  the  “  personal  equation.”  All 
tests  for  commercial  purposes  should  be  such  as  to  eliminate,  as  far 
as  possible,  the  ‘‘  personal  equation.” 

In  concluding  this  lecture  I  should  like  to  add  that  this 
branch  of  the  subject  concerns  the  papermaker  and  stationer 
alike,  but  has  not  yet  received  much  attention.  The  information 
is  fragmentary  and  scattered.  In  some  cases  the  conclusions  arrived 
at  by  different  investigators  are  contradictory.  The  information 
at  present  savours  too  much  of  the  scientist  and  too  little  of  the 
practical  man.  What  is  wanted  is  systematic  study  and  daily 
records,  which  in  course  of  time  will  become  yearly  records.  The 
records  must  be  accurate,  and  care  must  be  taken  that  conclusions 
must  be  arrived  at  only  after  plenty  of  records  have  been 
accumulated  and  carefully  examined.  The  subject  does  not 
concern  the  present  so  much  as  the  future.  It  is  a  subject 
which  might  well  occupy  the  attention  of  the  National  Physical 
Laboratory,  but  I  venture  to  think  the  large  stationers  and  pub¬ 
lishers  of  this  country  would  do  well  to  put  someone  to  carry 
out  a  systematic  series  of  researches,  with  a  view  all  the  time 
to  attaining  some  practical  object,  and  with  a  view  to  finding 
out  exactly  “  where  they  are  ”  with  the  papers  that  pass  through 
their  hands  into  those  of  the  general  public,  and  further  with  the 
view  of  ascertaining  in  each  case  the  most  suitable  paper  for 
each  of  the  multifarious  purposes  to  which  paper  is  put. 


INDEX 


A 

PAGE 

Acid  action  of  drawing  papers  ...  ...  ...  ...  ...  ...  124 

Acidity,  influence  of  ...  ...  ...  ...  ...  ...  ...  76 

,,  and  alkalinity  of  different  papers  ...  ...  ...  ...  99 

Art  paper  .  ...  .  ...  .  ...  19,  32 

,,  imitation...  ...  ...  ...  ...  ...  ...  ...  31 

Ash  ...  .  ...  .  ...  .  15 

,,  purity  of  ...  ...  ...  .  76 

Atmosphere,  the  ...  ...  ...  ...  ...  ...  ...  51,  116 

B 

Banknotes  .  .  136 

Behaviour  of  iodide  paper  ...  ...  ...  ...  ...  ...  98 

Beating  ...  ...  ...  ...  ...  ...  ...  ...  ...  109 

Bleaching,  chemistry  of  ...  ...  ...  ...  ...  ...  ...  49 

,,  “circulating”...  ...  ...  ...  ...  ...  ...  57 

,,  early  history  of  ...  ...  ...  ...  ...  ...  49 

,,  effect  of  atmosphere  on  ...  ...  ...  ...  ...  54 

,,  in  beater  ...  ...  ...  ...  ...  ...  ...  42 

,,  Hermite  ...  ...  ...  ...  ...  ..  ...  55 

,,  due  to  lime  salts  ...  ...  ...  ...  ...  ...  76 

,,  liquor,  continuous  use  of  ...  ...  ...  ...  ...  59 

,,  ,,  temperature  of  ...  ...  ...  ...  ...  60 

, ,  powder,  change  of  strength  on  storage .  39 

,,  ,,  relative  efficiencies  of  ...  ...  ...  ...  46 

,,  ,,  table  of  strengths  ...  ...  ...  ...  39 

,,  ,,  storage  of  ...  ...  ...  ...  ...  ...  39 

,,  solution,  effects  of  carbonic  acid  gas  on  ...  ...  ...  43 

,,  “still”  .  56 

,,  sun  ...  .  ...  ...  ...  .  50 

,,  tumbler  ...  ...  ...  ...  ...  ...  ...  42 

Blottings  .  .  ...  .  129 

Brittleness  .  .  107 

Bulk,  question  of  ...  ...  ...  ...  ...  ...  ...  ...  140 

,,  influence  of  glazing  on  ...  ...  ...  ...  ....  ...  140 

,,  effects  of  mineral  constituents  on  ...  ...  ...  ...  141 


147 

C 


Calendering 

Capillarity 

Carbonic  acid  gas,  effects  on  bleaching  solution 

Casein  . 

Caustic  soda,  impurities  in 
Cellulose 

, ,  expansion  and  contraction  of 

Characteristics  of  fibres  ... 

“  Chemical  News,”  references  to  . 

Chemical  condition  of  paper  .  . .  . 

,,  examination  of  paper 
Chemicals,  consumption  of,  on  boiling  ... 

, ,  iron  in 
Chemistry  of  rusting 
Chlorine  gas ... 

Chlorination... 

Chloride  of  lime,  nature  of 
,,  j)  as  powder 

,,  ,,  in  solution 

Church,  Prof.  A.  H.,  on  “Colour” 

Clay . 

Climatic  and  local  conditions  affecting  requirements 
Coating,  test  for 

,,  preparation  and  application  of 

Coated  surface,  nature  and  utility  of  ... 

Commercial  value  of  raw  materials 
Contamination  of  paper  from  raw  materials  ... 

, ,  , ,  iron  during  manufacture 

Curling  of  paper,  the 

D 

Damping,  effects  of 
Decay,  liability  to  ... 

Definition  of  paper... 

Deterioration,  cause  of 

,,  due  to  mechanical  wood... 

Dickinson  Institute 
Discharge  of  lines  ... 

Discoloration 

,,  by  sunlight  ... 

Drawing  papers 

,,  ,,  acid  action  of  ... 

Drying,  shrinkage  on 


E 

Eau  de  Javelles  . 

Elasticity 

Electrolytic  bleaching,  Hermite  ... 
Elimination  of  iron  during  manufacture 
“Encyclopaedia  Britannica”  reference  ... 


PAGE 
...  110 
...  106 
43 
22 
88 
11 
63 
35 

17,  55,  66,  85 
96 
28 
16 
83 
80 
41 
12 
37 

37 

38 

...  142 

...  115 

...  137 

23 
21 
29 
17 
87 
83 
65 


69 

121 

86 

113 

126 

33 

77 

116 

130 

138 

124 

104 


45 

103 

55 

83 

49 


148 


PAGE 

Expansion  and  contraction  of  cellulose  ...  ...  ...  ...  63 

Effects  of  heat  and  time  on  the  storage  of  bleaching  powder  ...  39 

,,  ,,  on  paper  ...  ...  ...  ...  ...  •••  63 

,,  iron  in  water  ...  ...  ...  ...  ...  ...  •••  82 

,,  different  materials  added  to  the  chest  .  90 

,,  metallic  residues  at  high  temperatures  .  97 

, ,  water  on  fibres  ...  ...  ...  ...  • .  ■  •  •  •  •  ■  •  102 

,,  rosin  ...  ...  ...  ...  •••  •••  •••  108 

,,  damping...  ...  ...  ...  ...  ...  ...  •••  69 

Examination  of  rags  .  .  17 

,,  methods  of .  .  .  119 

,,  chemical  and  physical  ...  ...  ...  ...  ...  28 

,,  for  nitrogenous  matter  ...  ...  ...  ...  ...  119 


F 

Fading  of  water  colours  ... 

Felting  qualities  of  fibres . 

Fermentation  . 

Fibres,  nature  of 

,,  physical  properties  of  . 

,,  the  effects  of  the  . 

,,  the  lasting  qualities  of  . 

,,  fixation  of  lime  from  water  by  ... 

, ,  peculiarities  of  ultimate . 

,,  relative  lengths  of... 

,,  effects  of  water  on . 

,,  Indian 

Flexibility  ...  ...  . 


116 

104 

119 

20 

110 

115 

128 

89 

34 

35 
102 

9 

103 


G 

Gelatine  or  glue  . 

,,  sizing  effect  on  strength 

Germany,  work  in . 

Glazing 


...  23,  83 
...  125 

...  132 

140 


H 

H.M.  Stationery  Office  contracts  . 

Hermite  bleaching  . 

Herzberg  on  “  Paper- testing  ”  . 

Hughes,  Mr.  E.,  on  “Water  as  a  catalyst”  ... 
Hydraulic  pressing,  influence  of  temperature  on 


132 

55 

67,  128 
98 
105 


I 

Iodide  paper  . 

Imitation  art  paper 
Improvement  on  storage  of  paper 
“  Imperial  Institute  Journal,”  reference  to 
Indicators 

Indian  and  Colonial  Exhibition . 


98 

31 

138 

11 

93 

9 


149 


PAGE 


Influence  of  acidity  .  76 

,,  rosin  and  gelatine  sizing  on  strength  ...  ...  ...  125 

,,  glazing  on  bulk  ...  ...  ...  ...  ...  ...  140 

,,  glazing  on  appearance  ...  ...  ...  ...  ...  141 

Insoluble  constituents  of  paper  ...  ...  ...  ...  ...  ...  97 

Italy,  work  in  .  ...  135 

Iron  in  chemicals  ...  ...  ...  ...  ...  ...  ...  83 

,,  in  finished  papers  ...  ...  ...  ...  ...  ...  ...  83 

,,  reasons  for  presence  of  .  .  78 

,,  amount  in  raw  materials  ...  ...  ...  ...  ...  ...  79 

,,  effects  of,  in  water  on  paper  ...  ...  ...  ...  ...  82 

,,  elimination  of,  during  manufacture  ...  ...  ...  ...  83 

,,  test  for  ...  .  S3 

,,  and  other  metallic  particles  ...  ...  ...  ...  ...  85 


L 


Light,  action  of,  on  papers  ...  ...  ...  ...  ...  ...  141 

Lime  salts  due  to  bleach  ...  ...  ...  ...  •••  ...  76 

„  boiling  .  87 

,,  fixation  of,  from  water  ...  ...  ...  ...  ...  ...  89 

,,  chloride  of  ...  ...  ...  ...  ...  ...  ...  37 

Little,  A.  D.,  reference  to .  68 


M 

“  Machine”  and  “  cross  ”  direction 
Mather  patent  open  bleach  system 
Martens 
Metallic  salts 

,,  residue  at  high  temperatures 
Moisture 

,,  “sensible”  . 

Minerals  used  for  coating ... 


N 

National  Physical  Laboratory  .  134 

Nitrogenous  matter  .  119,  121 

Non-cellulose  ...  ...  ...  ...  ...  ...  ...  ...  11 


O 

Opacity  .  143 

,,  necessity  for  uniform  method  ...  ...  ...  ...  145 

Organisms  .  119 

Ozone  . 50,  61 


67 

50 

128 

76 

97 

13,  64,  118 
64 
21 


150 

P 


“  Paper  and  Pulp  ”  . 

PAGE 
8,  21,  138,  145 

“  Papermaker,  The  ”  ...  . 

.  126 

“  Paper  Trade  Review  ”  . 

“  Papier  Zeitung”  . 

135,  144 

.  23 

Paper,  action  of  light  on . 

.  141 

,,  art  ...  " . 

. 19,  32 

,,  blotting 

.  129 

,,  curling  with  change  of  moisture 

... 

65 

,,  contamination  of 

.  87 

,,  chemical  condition  of 

.  96 

,,  definition  of 

.  86 

,,  drawing  ...  ...  . 

124,  138 

,,  discoloration 

.  130 

,,  iodide 

.  98 

,,  imitation  art 

.  31 

,,  insoluble  constituents 

.  97 

,,  opacity  of  ... 

.  143 

,,  permanence  of 

.  113 

,,  soluble  constituents 

.  97 

, ,  storage  of  ... 

. 138 

, ,  mode  of  testing 

.  92 

Photography  as  applied  to  illustration  printing 

.  24 

Preservation,  early  attempts  at 

.  113 

Process  blocks  . 

.  24 

R 

Rags,  examination  of 

.  17 

Raw  materials  ...  ...  . 

...  7,  17,  79,  87 

Relative  efficiencies  of  different  solutions 

.  46 

Results  of  physical  tests . 

.  28 

Rosin,  effects  of 

.  108 

Rusting,  chemistry  of  . 

.  80 

,,  prevention  of 

.  81 

S 

Scavia,  Dr. 

.  136 

Schmidt’s  American  patent 

.  24 

Sizing 

115,  125 

Society  of  Arts 

“  Society  of  Chemical  Industry  Journal  ” 

...  8,  123,  125 

. 23,  24 

Soluble  constituents  of  paper 

.  97 

Shrinkage  on  drying  . 

.  104 

Strengths,  table  of 

.  39 

Sun  bleaching 

.  50 

Sunlight,  action  on  paper  . 

...  52,  116,  130 

Surface  coating,  nature  and  utility  of  ... 

.  29 

Storage  of  bleaching  powder  . 

.  39 

,,  Paper  . 

.  138 

Stretch  and  strength  of  paper  . 

.  139 

Stationery  Office,  H.M.,  contxacts 

.  132 

Sweden,  work  in 

.  137 

151 

T 

PAGE 

Table  of  strengths  ...  ...  ...  ...  ...  ...  ...  ...  39 

Temperature  of  bleach  liquor  ...  ...  ..  ...  ...  ...  60 

,,  when  hydraulic  pressing  ...  ...  ...  ...  ...  105 

,,  and  moisture  ...  ...  ...  ...  ...  ...  118 

Test  for  coating  ...  ...  ...  ...  ...  ...  ...  ...  23 

,,  „  “machine”  and  “cross”  direction  .  67 

,,  ,,  iron  ..  .  83 

,,  ,,  paper  .  ..  ...  92 

,,  physical  on  art  papers  ...  ..  ...  ...  ...  ...  27 

Thompson’s  process  ...  ...  ...  ...  ...  ...  ...  43 

Transparency  of  papers  ...  ...  ...  ...  ...  ...  ...  143 

Tumbler  bleaching...  ...  ...  ...  ...  ...  ...  ...  42 

U 

United  States,  work  in  ...  ...  ...  ...  ...  ...  ...  137 

Uniform  methods,  necessity  for .  ...  14o 

W 

Water  ...  ...  ...  ..  ...  ...  ...  ...  82,  102 

Water  colour  fading  ...  ...  ...  ...  ...  ...  ...  116 

Winkler,  0 .  .  131,  144 

Y 


Yield  of  cellulose  ... 


...  12,  14 


ADVERTISEMENTS. 


153 


C.B.S.  Units  ^  ^  ^ 

OR 

Standard  Paper  Tests. 


An  Essay  towards  establishing  a 
Normal  System  of  Paper  Testing. 

BY 

C.  F.  Cross,  E.  J.  Bevan,  Clayton  Beadle, 

-Hr  AND 

R.  W.  SlNDALL. 


“  The  special' subject  discussed  has  very  important  practical  bearings, 
since  the  buying  and  selling  of  papers  must  be  more  and  more  regulated 
by  standards  of  quality  such  as  can  be  expressed  in  terms  of  physical  and 
chemical  measurements  or  estimations.” — Vide  Preface. 


Pries  2/8  Post  Free. 


Published  by  .  .  . 

WOOD  PULP,  Limited, 

10,  Godliman  Street,  LONDON,  E.C. 


154 


ADVERTISEMENTS. 


“Paper  and  Pulp.” 


A  Fortnightly  Journal  for  the  PAPER,  .  .  . 

.  .  .  PULP,  and  ALLIED  TRADES. 

Published  on  the  1st  and  15th  .  , 

of  each  Month  10/-  per  annum,  Post  Free. 


McNAUGHTON'S 

‘ Factory  Book=Keeping 

for  Paper  Mills 


A  PRACTICAL  SYSTEM  OF  .  . 
BOOK-KEEPING  AND  COSTING. 


10/-  Post  Free. 


BEVERIDGE’S 

“ Papermakers ’  Pocket  Book.” 

Concise  information  relating  to  the  Engineering, 

Chemical,  Office,  and  Papermaking  Departments  10/-  Post  Free. 
of  the  Paper  Mill. 


C.B.S,  Units  or . . . 

Standard  Paper  Tests. 

By  CROSS,  BEVAN,  BEADLE,  and  SINDALL. 


AN  ESSAY  TOWARDS  ESTABLISHING  A 
NORMAL  SYSTEM  OF  PAPER  TESTING. 


2/8  Post  Free . 


ADVERTISEMENTS. 


155 


M.M.C.  MOTORS 


ENGLAND’S  BEST. 


MOTOR  CARS  for  Commercial  Travellers. 

9  GOLD  MEDALS. 

MOTOR  CARS  for  Business  and  Pleasure. 

MOTOR  VANS. 


11  SILVER  MEDALS. 


2  BRONZE  MEDALS. 


MOTORS  for  Electric  Lighting,  Pumping,  and 
all  Purposes  where  powers  up  to  35  h.p. 
are  required,  and  simplicity  and  economy 
of  space  are  objects. 


M.M.C.  MOTORS  have  been  awarded  Medals  for  four 
years  in  succession  in  the  Automobile  Club’s 
Reliability  Trials. 


MOTORS  from  3  to  35  B.H.P. 


For  full  particulars  apply  to — 

THE  MOTOR  MANUFACTURING  CO.,  Ltd., 


95,  NEW  BOND  STREET, 
LONDON,  W. 

Works:  Telephone:  5556,  GERRARD. 

COVENTRY.  Telegrams:  “PROPEL,  LONDON. 


Estimates  on  Application. 


156 


ADVERTISEMENTS. 


JAMES  MILNE  &  SON,  u* 

=  -  Engineers,  -  - 

Milton  House  Works,  EDINBURGH. 


HIGH-SPEED  PAPER  MACHINES, 
OF  UP-TO-DATE  DESIGN 
AND  PERFECT  CONSTRUCTION, 
WITH  ALL  ACCESSORIES. 


ANGLE  PAPER  CUTTER. 


Telegrams:  MILNE,  Edinburgh.” 


Repairs  &  Renewals  carefully  carried  out. 


ADVERTISEMENTS. 


157 


Combined  Patent  Vacuum 


AND 


Back-Water  Arrangement. 


AT  WORK  IN  THE  FINEST  MILLS  IN  BRITAIN 
WITH  THE  GREATEST  POSSIBLE  SUCCESS. 


One  Mill  with  four  Machines,  four  with  three,  and 
several  two-Machine  Mills  have  nothing  else  on  their 

Machines. 


Two  Centrifugal  Pumps  complete  the  whole  Pumping 
arrangements  of  a  modern  Machine. 


ABSOLUTE  SIMPLICITY— POWERFUL  AND  =  = 
CONSTANT  VACUUM— WASHING  UP  MINIMISED. 


The  Users  say  they  are  the  best  thing  that  has  been  introduced 
to  Machines  for  years. 


BERTRAMS  LIMITED. 


158 


ADVERTISEMENTS. 


MW  PATENT  ROPE  DRIVE. 

Gives  thorough  control  of  the  draws  of  paper  throughout  the 
papermaking  machine. 

Absolutely  regular  and  smooth  running  without  any  jerking 
motion. 

Extreme  simplicity  of  details,  which  simplicity  is  not  lessened  in 
the  complete  drive  necessary  for  the  largest  machines. 

Goes  into  the  least  possible  space. 

Only  one  rope  needed  to  drive  machine  from  couch  rolls  to  reel. 


PATENT  EXPANDING  ROPE  PULLE'i 

FOR  SECTIONAL  DRIVINC  OF  PAPER  MACHINES. 

Code  Word  “  EXPANSU/fe.” 

BERTRAMS  LIMITED,  ENGINEERS,  SCIENNES,  EDINBURGH. 

Automatic  stretching  arrangement  takes  up  slack  of  rope,  and 
that  when  the  rope  is  not  under  the  tension  of  power  exerted. 

No  cumbersome  parts  to  lift  or  lower  when  stopping  or  starting 
any  section  of  the  machine,  the  stopping  or  starting  of  each  section 
being  effected  without  any  skidding  of  a  pulley  on  a  belt. 

No  overhead  shafts  nor  bevel  gear  necessary. 

For  a  machine  having  say  eight  sectional  drives,  only  16  bearings 
are  necessary  on  entire  shafting  from  couch  roll  to  reel. 


Sole  makers:  BERTRAMS  LIMITED 


WURSTER’S  PATENTED 


ADVERTISEMENTS 


159 


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Does  double  and  four  times  the  work  of  stones,  but  does  not  shorten,  affect, 
crease,  or  wet  the  Fibre  in  any  way,  nor  change  the  colour  or  the  Sizing. 
Can  also  be  used  for  Kneading  Clay  and  other  Fillers,  as  well  as  for  Kneading 
Dry  Bleaching-powders,  instead  of  the  Bleaching  Mill, 


PAPER-TEARING  MACHINE, 


160 


ADVERTISEMENTS, 


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ADVERTISEMENTS. 


i  v 


PEARSON  &  BERTRAM’S 

PATENT 

Refining  Engine. 


AT  WORK  ON  ALL  CLASSES  OF  - 
PAPER,  AND  THE  SIMPLEST  AND  - 
MOST  EFFICIENT  IN  CONSTRUCTION. 


Greatly  .  . 
lessens  time 
required  for 
pulp  in  .  . 

Beaters,  and 
increases 
output. 

Makes  closer 
wove  and  . 
dearer  laid 
papers. 

Reduces  .  . 
broke  to  a 
minimum. 

Thoroughly . 
assimilates  . 
all  classes  of 
pulp. 

*  * 


SOLE  MAKERS— 

BERTRAMS  LIMITED. 


V 


ADVERTISEMENTS. 


“The  Grosvenor  .  . 
Engineering  Works.” 

MACHINISTS. 

EXECUTED  TO  ANY  CLASS 
I\VpdiI  5  OF  MACHINERY  AT  .  .  . 

.  .  Moderate  Rates. 

_ 

Petrol  Motors 

of  2?  B  H  P  to  25  B  H  P 

Supplied  for  Electric  Lighting  and  other 
purposes. 

Telegrams:  "DEPICTION/  LONDON.  Telephone  No.  1223,  KENSINGTON 

Danvers  St.,  Chelsea,  London, 


advertisements. 


VI 


-I- 


ESTABLISHED  1845. 


LIMITED, 

^RglKeePg,  -96- 

LEITH  WALK  FOUNDRY,  EDINBURGH. 

Telegraphic  Address—"  BERTRAM,  LEITH.” 


*  »  ♦ 


PAPER-MAKING 

MACHINERY  at 


GETTY  CENTER  LIBRARY 


ITS  BRANCHES. 


mm. 


